How to Recharge Alkaline Batteries

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About a month ago, I learned that it was possible not not only to test old alkaline batteries to see if they are still are usable, but also that, with the right type of charger, you can bring dead batteries back to life and that you can actually recharge alkaline batteries.  To be quite honest, I was blown away.

Being a dutiful citizen of the world, when a flashlight. computer mouse, or portable  electronic gizmo such as a remote control stopped working, I dumped the old batteries into my recycle box and installed some new ones.  Of course not being wasteful, I favored the use of rechargeable batteries and was quite proud of my collection of various sized eneloop batteries which hold their charge for up to three years, even while sitting on the shelf.

Recharged Alkaline Batteries - Backdoor Survival


Do you every get a bug in your bum and decide that nothing will stop you from the mission or task at hand?  Well that was me.  I wanted to prove to myself that old alkaline batteries were still usable and further, as Dennis Evers (Preparedness is Fundamental) says, you can have free batteries for life.

The first thing I needed to do was to gather up the gear:

Old “dead” alkaline batteries
Battery tester simple enough to use without a PhD in electronics
Battery charger designed specifically for alkaline batteries
Test gear such as flashlights, remote controls, wireless headphones and more

Simple enough although I did have to purchase the tester and the charge.  But more on that later.


For years I have been saving all of my old batteries in a box in the garage, thinking that one of these days I would find someplace to recycle them.  Where I live that is easier said than done so the box was pretty darn full which was great because that meant I had a lot of raw material to work with.

Batteries to Recycle

My Box of “Dead” Batteries

While waiting for my battery tester and alkaline charger to arrive, I sorted through the box, weeding out any leakers as well as odd ball batteries such as cell phone and hearing aid batteries.  According to Wikipedia, the reason a battery leaks is this:

As batteries discharge — either through usage or gradual self-discharge — the chemistry of the cells changes and some hydrogen gas is generated. This out-gassing increases pressure in the battery. Eventually, the excess pressure either ruptures the insulating seals at the end of the battery, or the outer metal canister, or both. In addition, as the battery ages, its steel outer canister may gradually corrode or rust, which can further contribute to containment failure.

Leaked Battery

Leaked Battery – Yuck

Surprisingly, most of the batteries in my box were clean.  Something to keep in mind as you go through the sorting process is that if there is even a single leaker in the box, the residue can spread on to other batteries so it helps to have a rag handy to wipe each battery off to see if it is okay.  If you even suspect that a battery has leaked, or if shows any rust or corrosion, don’t take a chance.  Throw the baddies back in to the recycle box.


I purchased an inexpensive battery tester from Amazon.  There was nothing special about it and it was easy to use.  Plus, it had the ability to test 9V batteries as well as button batteries and the traditional AA, AAA, C and D sized batteries.

Simple and Cheap Battery Tester

Simple Battery Tester

I then set to work, testing each and every battery in my box.  Much to my surprise, there were a number of batteries that tested “fully charged”. It is interesting to note that many were 9 Volt batteries that came out of one of my carbon monoxide detectors. This leads me to believe that the detector is bad and not the batteries.

Furthermore, I now believe that what commonly happens is that, for example, a remote control or flashlight is dead.  You dump the batteries into the recycle box and install new ones.  Easy peasy.  But in truth, perhaps only a single battery of the 2 or 3 are bad so in effect, you are dumping out 1 discharged battery and 2 or 3 perfectly usable batteries.  I even proved this myself.  Since I now keep one of these $8 testers in my desk drawer, when my wireless mouse died a couple of days ago, I found that only one of the two AAA batteries that I had removed was dead.  The other was showing almost a full charge.  Go figure.

The other thing, and something that makes me feel careless and stupid, there were some perfectly good rechargeable batteries in the box.  Now how the heck did that happen?

Good Batteries

These were good!

Batteries test fine in the mini MAGLITE

And I thought these batteries were dead.


After reading reviews on various rechargers, I settled on the Maximal Power FC999 Universal Battery Charger.  It wasn’t the most expensive available but according to a couple of the reviewers, this unit was exactly the same as a higher priced model.  The difference was that this one is black and the other one was gray.

Maximal Power battery charger from Amazon

Maximal Power FC999 Universal Battery

Now here is the deal with this charger.  It has four separate charging chambers that operate independently of each other.  This means that you can mix and match battery sizes (AA, AAA, C, D) without a problem.  It also has a center 9V battery chamber but I have not been able to figure out whether that piggy backs upon one of the adjacent chambers or whether it operates separately.

Note:  this charger can also be used to charge Ni-cd and Ni-MH batteries but I only tested it on Alkaline batteries.  There is a slider switch that allows you to select the type of batteries you are charging – they can not and should not be mixed and matched by type (although, as I mentioned, various sizes of the same type work just fine.)

There is no question that I experienced a bit of trepidation when I inserted the batteries into the charger for the first time.  But there was no smoke and no explosion so I continued on.

A few seconds after you insert the batteries, the tester will recognize the status and the LED window will either say “CHA” (for charging) or “BAD” (for sorry, this is a bad battery and it cannot be charged).  In addition, the following lights will glow:

  • Red – Charging
  • Green – Fully Charged
  • Red Flashing – BAD

As I mentioned above, each of the four chamber operates independently so you could have a combination of these three options all going at once.

There is a chart in the manual that indicates that a AAA battery will take 2.5 hours to charge, a AA 5 hours, a C size 6 hours, and a D sized 10 hours.  In my experience, however, they charge to the fully-charged, green light stage a lot sooner then that.  Now here is the thing.  Once fully charged, the charger switches to a trickle charge to keep the battery “at its optimum capacity” whatever that means.

My experience is that if you leave the recharged batteries in the charger overnight – or say for about 10 or 12  hours – you will get a much stronger charge.  I say this because I first tested some batteries right after the green light came on.  On my tester, they would register at about the half way mark in the fully-charged area.  If I put them back in the charger, the green fully-charged light would come on right away but when I took them out the next morning, the tester showed them about 90% charged.

Recharged Alkaline Batteries

These batteries have been re-charged and are now usable

After doing this a few times, I realized that next on my bucket list was a tester that would give me the actual voltage of the re-charged battery.  My brother and nephew – both electronics wizards – have one and tell me that is the only way to truly test the remaining juice left in a used battery.


The little manual that came with the charger stated that alkaline batteries can be charged to 75 – 90% of their original capacity.  It further said that the batteries should be fully drained before recharging but I found that as a practical matter, the fully drained batteries came up “BAD” and could not be recharged at all.

There is one more rather important note that I want to make.  I checked on my recharged batteries about two weeks after storing them in a box in my utility cupboard.  Much to my surprise there were some new leakers.  Now whether these were overlooked initially (had I wiped away the residue not realizing they were compromised) or a byproduct of the charging process – I do not know.  Even more curious, they were all the Costco Kirkland brand batteries.

Alkaline Battery after recharging

I had good luck charging the Duracell batteries

The manual also indicates that alkaline batteries should not be recharged more than 30 times. 30 times – holy moly – that seems like a lot of charging to me.  For now, I will charge them once until I go through the pile and then start anew.  But 30 times?  I am going to play it safe and protect my devices by recharging no more than a dozen times if that.


Using the recharged batteries on low power devices such as mini LED flashlights and of course, my computer mouse, worked great.  As a matter of fact, I can not tell the difference between the recharged Alkalines and standard rechargeables.  On the other hand, the Survival Husband uses wireless headphones to watch TV and the recharged alkalines only last abut 8 hours as opposed to the typical 15 to 20 hours with standard Ni-mh rechargeables.

flameless candle

Flameless candles have burned steadily for 5 days

The recharged 9V battery worked especially well on my little Blocklite flashlight.  This little flashlight has been on 24/7 since March 9th and today for the first time I noticed the LEDs starting to fade when all six LEDs are on. When I turn the switch to 2 LED mod, it is as bright as ever.

blocklite flashlight

Blocklite Mini Flashlight in Day 7

Clearly, for now at least, it appears that the recharged alkaline batteries are are best suited for low-drain devices.


I purchased these inexpensive storage cases for my recharged batteries. They are really quite handy and I like that the six individual cases interlock and connect together to make a larger case.  The rest of my spares are in the plastic pencil case you see pictured above.

Battery Case 002

I like these mini storage cases.


For a total investment of about $34 I now have what for all intents and purposes, a lifetime of free batteries.  The reason I say “lifetime” is that my friends have indicated an willingness to give me all of their dead batteries and you can bet that many will still be either good as is or eligible for recharging.

Would I trust these recycled batteries in a survival situation – sure, if that is all I had,  But of course, that is not the case.  I still have a large supply of brand new alkaline batteries in all sizes plus a good supply of standard rechargeables (you know how I love those eneloop rechargeables).

But as spare batteries to use day to day, heck, these are great.  As my tests have proven, a recharged alkaline battery can keep a small LED flashlight going to over a week and a computer mouse for much longer than that.  As a matter of fact, you might say I have become obsessed with using these recharged alkaline batteries.  But that, of course, is a story for another time.

Enjoy your next adventure through common sense and thoughtful preparation!

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Bargain Bin: Here are links to the products mentioned in today’s article.  I do hope you will consider the battery tester – it will definitely pay for itself by preventing you from recycling perfectly usable alkaline batteries.

Maximal Power FC999 Universal Battery Charger: This nicely built charger will charge charge AA, AAA, C, D, N, 9V, Ni-MH, Ni-CD, and Alkaline batteries. It has an LED display so that when you first put a battery in the charging bay, you know whether it is viable for charging or simply bad and ready to go back to the recycle box. Note: When I purchased the charger, it was on backorder. Oddly, it actually shipped the next day. Go figure.  Anyway, I am really sold on this charger and can recommend it without reservation,.

Blocklite 001

Blocklite Mini Compact Size Ultra Bright 9V LED Flashlight: One of my readers (James) turned me on to these nifty little LED flashlights.  They were great with re-charged 9V batteries. There is a similar flashlight called the Pak-Lite (which is more expensive) but it does not have a high-low switch like this one. Less than $10.

SE BT20 9-Volt Battery Tester  You definitely should consider a battery tester even if you decide not to re-charge your alkalines.  The advantage of having a tester is that when a gizmo dies, you can determine whether just a single battery is discharged and not the complete set.

SODIAL(TM) Battery Tester Volt Checker for 9V 1.5V and AA AAA Cell Batteries:  This tester has a numeric display – something worth considering although may take two to three weeks to arrive.  As I write this, it is only $4.00 with free shipping.

AA / AAA 4 Cell Battery Storage Case (Bundle of Six Cases):  I like these little cases.  I put a sticker on the outside of the case indicating that these are re-charged batteries.  About $6 with free shipping.

And for traditional rechargeable batteries:

Solar 11-in-1 Battery Charger: This is a universal charger that does what it is supposed to do. It uses sunlight to generate a current that charges pairs of batteries in sizes AAA, AA, C, or D and works great with my favorite eneloop batteries.

Sanyo Eneloop 1500 Super Power Pack: This kit has it all, including 12 AA, 4 AAA, 2 C and D Spacers, a 4 position charger and storage case. This is the kit that I own.


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How to Recharge Alkaline Batteries — 62 Comments

  1. Wow! What a great idea on the batteries! Like you, I also had a recycle battery box that made it’s way to our local recycle center. I am going to give this a try. I didn’t even know they made a charger that recharged regular batteries.

    • Yes it does. It also tests those pricey button batteries. You can not recharge the button batteries but you can find “good” ones that are still usable in the recycle box (or at least I did).

  2. gaye: one thing i notice is the random organization of batteries in your larger boxes. please be aware that batteries with any charge left in them can be a fire hazard if they complete a circuit. this can happen especially with 9-volt batteries that come in contact with something metal, like a paperclip. i’ve seen news stories where people’s junk drawers spontaneously burst into flames because of spare batteries touching metal. you are best to organize your spare batteries (recharged or for recycling) into rows all facing the same direction, and with a piece of cardboard between each layer. something like this photo. just wanted to share with you.

    • Thank you so much for this advice. As I was pondering why a few had started to leak – I mentioned this in the article – I began to wonder if it had something to do with the way they were being stored. I need to get some more of those little battery cases that I like so much. In the meantime, I have taken them out of the box and laid them out on a towel with nothing touching. Thanks again. I plan to pass this info on to my readers in the Sunday Buzz as well.

      • you can still keep them in cardboard boxes (no metal), i just suggest keeping them all facing the same direction and layers or rows separated by more cardboard. don’t know if this has any effect on the corrosion/leaking or not. other suggestions for inexpensive storage are tackle trays, sewing or drawer organizers with little compartments. i personally like small cardboard boxes, shoeboxes, etc, because they’re free and stack easily.

        • You can also put a piece of tape (I use duct tape) over the contact ends so they can’t touch metal and short across to start a fire. This is for 9 volt batteries which are usually the culprits that start fires but it will work on all.

    • This was the first thing I thought as I saw that picture of that box of batteries. “WOW what a fire hazard!” Seems Gaye caught it, either from you or when she noticed the pic in her article. Sometimes a photo clicks something within us which gives us an extra perception. 😉

  3. Thanks for the info. Have not come across these issues yet but I am living off grid for last 6 years and have solar system with L-16 battery bank. Will be back often for more great information. Thanks George

  4. thank you for an excellent well written,well thought out, useful article, to take it a step further, any thoughts on solar chargers?

    • I am in the process of testing a compact solar charger for my electronic devices (cell phone, computer and iPad) but so far the sun is not cooperating. I have not used a solar battery charger yet for the same reason but will add that to the bucket list for later in the Spring.

  5. Let me know how it goes. Currently I am charging all of my phones, screwguns, etc from the wall outlet that is fed by the six 225 watt panels that power my frig and all other electrical appliances in my home. When I climb 14,000 foot peaks I could definitely use a portable charger. Thanks for your info. I will be waiting anxiously for your next report. Please give me brand info on your results.
    Thank you

  6. Hello to all who are recharging alkaline batteries.
    As a knowledgeable electronic type I want to put a little “professional” spin on the battery situation. The fact that you have worked out a recharging program is good. The first thing I want to say is the recharged batteries may not have the same power capacity they did when brand new. Each time one is successfully recharged it will loose a bit more available power. They won’t last or recharge forever.
    One poster mentioned the fire hazard of storing loose batteries. Yes keep them all lined up in the same direction with the cardboard spacers. 9 Volt batteries are the most dangerous to store loose. Put a piece of black electric tape over the terminals. If you bought the batteries in one of those 24 or 48 packs that would be a good place to restore them. One last comment a recharging battery could vent with some force so don’t have the charger located where it could cause harm.

    • Thanks for your insight, Bill. I have already reboxed my charged up batteries so they all line up in the same direction. I chose to only use one layer per box just to be on the safe side.

      Good tip regarding the electrical tape – I plan to share you tips on an upcoming Sunday Survival Buzz.

    • Thanks for that last comment. I’m currently using my charger. I’ll be rehoming it as I leave this site. 🙂 Gaye, this charger works great and like you, I told people I would take their old batteries off their hands. lol I so love the looks! Thanks again Bill.

  7. Wow, that is really interesting. Thank you so much for posting this. I had always thought that it should be possible, somehow, to re-charge batteries, even just the normal ones.
    Leaky fluid from batteries kind of scares me. I don’t know exactly why… it just seems like poisonous, disgusting chemical something. I think I’ll stay away from the Costco Kirkland batteries.

  8. I use a Burgess battery charger for NiCD and carbon-zinc batteries. It will charge 9 volt batteries in about 5 hours. I have been using it on 9 volt carbon-zinc batteries for smoke detectors and it works fine. I check the voltage on the charger with my volt meter and it showed that it was only charging at about 1 volt. So far all of the 9 volt zinc-carbon batteries work fine in the smoke detectors. Now I wait until one start beeping and switch in 9 volt from my stockpile and recharge the old one. Much better than buying 9 volt batteries once a year. I do not know how many times the carbon-zinc 9v batteries can be recharged but I have a bunch.

  9. Instead of purchasing specific type battery testers you might think about a voltage meter. You can get those at Wal-mart, Dollar General, Harbor Freight or about any place that sells tools, but these are the least expensive with a cost under $5. A voltmeter can not only test the voltage of any battery, but household voltage, test for shorts and more. I have found that certain irregular batteries like button type or a short AA called 2/3 AA, can be charged using some type of conductive material like a screw or bolt of the proper length to fill the space in the charger.

  10. So I did go ahead and buy the Burgess Battery Charger and proceeded to recharge the coffee can full of dead AA and AAA. Everything looks good – the charge meter I bought says they are recharged. I stored the re-charged batteries in empty plastic pill containers. I went to use some the other day and there was some kind of clear fluid leaking from the batteries – I checked all the containiers I had, 5, and they all had the same clear, viscus fluid coming from the batteriers. I dont know if all the batteries were leaking of not. Needless to say I did not and will not use the batteries in any of my electronics. Has anyone else had this happen after recharging alkaline batteries? Needless to say I will not try recharging alkaline batteries again.

    • Prepperdaddy – The only problem I have had is with the Costco Kirkland brand batteries. They are leaking some sort of white powder stuff and so I have not used them (nor will I purchase them again). This has happened to me with those Costco batteries even without re-charging them. There have been times when I open up my flashlight to change batteries and find that they have leaked inside making a big mess. I was glad they were not in my expensive electronics.

      BTW, in my more expensive devices I still use the Sanyo Eneloop rechargables – those are the best.

      Another thing is that my charger is a Maximal Power and not a Burgess.

      You do have me wondering if all of your batteries were of a single brand. Other than the Costco brand, I have had no additional leakers. The Duracells seem to hold the charge the longest but that may simply be my perception.

  11. Hi Gaye…

    I was wrong about the charger, I checked my old orders on Amazon and I did get the Maximal Power FC999. I also buy all by batteries at Costco but I don’t get the Kirkland brand…I get the other name brand they sell…is it Energizer??? In any event, it was the ‘good’ brand that was leaking some kind of goo from the bottom of the battery. I will be buying some good quality rechargeable from now on…the Eneloop look good. Thanks…nice to know you don’t write once and forget. Tell your good friend George that if he wants to stop his Gout, he needs to eat a Fat Free Yougurt every morning..he wont listen to me..:-)

  12. Gayle, I learned about batteries while doing the boating live-aboard thing. All batteries test full after charging; they are now at about 65- 70% full. Leave them on trickle 8-12 more hours, and fill them up. Also, high drain and high charge cause them to leak quicker. You can lacquer seal them to prevent the worst of this. Try clear fingernail polish, and Do Not cover the terminal dots. If you want more info, try the boating battery books.

  13. Gaye, there is one other battery type in both AA and AAA sizes that is rechargeable — and very interesting because of its slightly higher voltage. (I just tested one at random with a voltmeter at 1.78 vdc.) It’s called a Nickel Zinc battery, and is abbreviated NiZn. Fry’s and Big Lots once carried them, but now I can only find them on eBay and Amazon (made in China). There is a special charger (sorry, not solar) sold just for them. That higher voltage does wonders for some things like pocket flashlights, battery powered shavers, etc. I haven’t found any gadget yet that the slightly higher voltage damages, but there may a surprise some day.

    Thanks for your insightful articles over the years.

  14. Just buy eneloops and do it right,they will safely and reliably recharge for years.They wont leak as essentially all alkalines do eventually.First time you ruin something with a leaking alkaline you will see this isnt the area you want to save pennies in.

    Buy eneloops and be done with battery issues for years.Making them quite cheap in the long run.

  15. First, I want to STRONGLY second the comments about not having the charger – OR the newly charged battery – anyplace where fumes, leaks, fire, or a small explosion could create a bigger problem. You are taking a small but nonzero risk of all of these by recharging a battery that was not designed to be recharged. Also, if the battery is even slightly warm to the touch after charging, it could be much hotter internally, and still may leak, vent, or even catch fire for a few minutes afterwards until it cools completely. I’d be wearing gloves and goggles while handling these things, just to be on the safe side. Especially goggles. Burns on skin will heal, but a damaged cornea might not.

    Second, I would strongly advise against ever recharging a 9v battery other than one designed to be recharged. It is different than the others in that it is actually six small 1.5v cells wired in series. Some of these will be weaker than others, and over time, will fail. Recharging it, then using it, can force current to flow through the bad cell in the wrong direction. This is the same reason why you shouldn’t mix old and new batteries in the same device, or batteries of different types.

    Finally, it pays to have a good quality battery tester. To test a battery properly, you need to test the voltage and/or current it provides under load and over some period of time. A weak battery can produce nearly the right voltage without any load, but that voltage will drop dramatically when connected to a load, due to high internal resistance. It also may properly power a load for a short time, but lose power rapidly during that time. Now, some people, realizing this, will just hook an ammeter across the battery terminals. This is a very bad idea because it can damage the battery, causing risks of fire, leakage, even explosion. A proper battery tester should place the battery under a moderate resistive load, leave it there for a period of time, measure the voltage drop initially and over time, and from those measurements, calculate: (a) the internal resistance of the battery and (b) the approximate amount of charge remaining. I don’t know if even a good tester will do this, but I know for sure that a crappy one won’t, and will therefore give misleading or incorrect information at least some part of the time.

    • I’d prefer charging Alkalines on a crank generator designed to charge batteries at a low mA rate to prevent the batteries exploding. You can stop periodically to allow the batteries to absorb the energy. I wouldn’t use the Alkalines in my Maglites or radios but they would offer something if they are able to hold a charge even for a little bit. Rechargeables would be the best for sure, but even some rechargeables burst leak and might even pop causing a fire. They are technically safer though because they are designed for charging while Alkalines can only take in a bit of a charge at a time. Charge them for too long, too high of a voltage/mA or throwing them in any charger is asking for trouble. If you get yourself a hand crank battery charger, you can stop for a little bit and then resume cranking, it stops the battery from heating up and reduce leakage. Batteries that leak like the wiki article states, generally happen from self discharging. Heat is another way the battery leaks, leaving them in your flashlight in the car will generally leak.

  16. Seriously?! 6 hours to recharge a battery that may last 8 hours in a low-demand device? If you want rechargeable batteries, why not just buy some good-quality Ni-Mh’s or Li-On’s? They’ll charge a lot faster; work a lot better; and you won’t be risking a fire every time you charge them! (Actually, the company who makes your charger- MaximalPower- makes great rechargeable batteries- including OEM-replacements for everything from tools to phones, which I have found to perform better than OEM- which is amazing, as most other after-market replacement batteries I’ve tried were junk)

  17. I have found that when my alkaline batteries show BAD on the charger I can usually “jump start them by connecting them to a small solar panel (1.5v), for 20-30 minutes. Then they show up as CHG on the charger and can be charged per normal. I suspect that any low-voltage DC power source would work. Experiment under safe conditions to prevent leakage, explosion, etc.).

  18. Hell, I discovered this fifty years ago when I suspected that the warning was a gimmick to keep you buying the expensive alkalines. Being a junior engineer, I just had to try it. It worked. BTW, I also had to find out why Jello warned us not to put kiwi fruit in their product. (The enzyme in it does not allow Jello to set up.)

  19. Some electronics will register a battery as dead if it is just low. Digital Cameras are a prime example. Once the battery starts loosing charge, it will stop working… when in fact that battery will work fine in other electronics.
    Thank you for a great article, I am on the search now for the charger and reader! We seem to go through a LOT of batteries with 3 kids!

    • Smoke detectors and carbon monoxide detectors are the worse but that is undoubtedly a good thing. I always use new batteries in them and save the recharged 9V batteries for flashlights and other devices.

  20. Gaye
    Great post. Commendable research on your part.
    I just replaced 12 AA batteries tonight in my 6 electronic candles on the family room fireplace mantel. Have to do that every 6 or 8 months or so.
    Also replaced 4 C batteries in my wife’s bedside combination flashlight, florescent light, flashing light and radio. This item rarely used, an emergency device, but needs batteries at least annually. I’m really considering the purchase of the FCC Maximal Power FC999 Universal Battery Charger.
    And then I read Joe’s comments on June 6,14. Being an EE myself, I know he is on target regarding safety. Those without knowledge of the risk involved by deviating from manufacturer’s recommendations for use/handling of electronic devices should not “do this at home”. My suggestion would be to go ahead with your suggestions on recharging batteries. But be careful not to disregard Joe’s comments with regard to safety. Get professional help if in doubt!

  21. Hello great thread with a few paranoid types chipping in LOL ..heres my c cents worth …I us a wireless tail tight set up that requires 4 AA on each Led light ..I went out and bought expensive Nicad energizer batterys the other day and they wont power the lights…why ? heres why Nicad rechargeable only supply 1.2 volts …alkaline toss outs make 1.5 ..I ntend to recharge some as the article tell you how too …NO FEAR …thanks Gaye !!

  22. My 2 cents worth regarding dead batteries appearing not to be dead when checked a while later – Many years ago we were investigating why our new low power parking meter design was actually using a lot less power, but the batteries were not lasting as long as in the older higher power design. After much research we discovered that the pin running from the negative terminal down the inside of the battery appeared to oxidise when there was not enough current being drawn through it. By simply ‘knocking’ the batteries we were able to brake the oxidation layer and the batteries where good for another few months. So there is merit to ‘banging’ your torch when it is dim or putting batteries in the sun to get another life out of them. We never explored the actual science behind the discovery and needless to say the big battery corporations didn’t bother responding when we enquired, so we changed to LiFePO4 rechargeables. So those ‘dead’ batteries are very often only ‘dormant’ and a good knock will ‘wake’ them up.

    • Hendrik – What a fascinating bit of information. I plan to give the “knocking” trick a go the next time my batteries test good but are not functional. I find this happens with one of my carbon monoxide detectors a lot which makes me think the unit and not the batteries are bad.

      • Is that like hitting your fruit tree with a bat several times as hard as you can to “wake it up?” I know it sounds strange but we had a pear tree that wasn’t producing fruit for several years and did this. The next year had fruit.
        Sorry, I know this isn’t about batteries, but it is about “recharging.”
        Ok, maybe I should be “hit” to get recharged. Hhhaaaaa….

  23. Costco batteries are the WORST. I had one explode in my fluke tester, and I had to clean it, and
    glue it back together.

  24. 2 Simple ways to recharge batteries.

    1) Over night
    Fill up a hot water bottle “Yes with hot water” fold it in half with the batteries in the middle of the fold, wrap it up tight in a quilt and leave overnight. FULLY CHARGED.

    2) 5 Min fix
    boil a cup of hot water, place batteries in a mug or cup, get a plastic bag with no holes and place in the mug poor hot water in the bag. Charged Batteries.

    This works 100% just allways check Batteries are not leaking, Iv’e never had any leaks in years of doing this but saftey1st.

  25. Throwing batteries into a box or bag, etc., may set your house on fire. It has happened. 9 volt batteries are particularly dangerous as the terminals are close together. Shorting the terminals may cause a fire, even if the battery is pretty well discharged.

  26. Just a bit more info, I was making chargers 20 years ago to charge Duracell batteries, the key to stop them overheating and exploding was for every mA put into the battery you had to remove a tenth of it,
    We did this in the UK by using an AC 50hz transformer a Diode and 2 resisters
    Resistors on the plus wave it loaded 200mA and on negative cycle removed 20mA, this method I was able to charge my Casio TV back up as quick as it drained.
    Crude diagram

  27. I have a bunch of yard lights purchased years ago. They
    are solar powered and eventually the NiCad batteries in them
    died. I was given a sack full of Costco AA batteries that came
    out of wireless Microphones which get used for several church
    services then replaced every week as they do not want failures
    during a church service. I put those batteries (kirkland) brand
    in my solar lights and they lasted months to a year … running
    all night and charging all day … not 10 times nor 30 times but
    hundreds of times. I got a free meter from Harbor Freight – it in
    in their ads regularly – actually I have one in every vehicle.
    I sort my free batteries by voltage I am not convinced that this is
    a good test and at a yard sale I bout a little VOM (volt ohm meter)
    for a $1 US that had a special battery test scale. I think that
    this actually puts a load on the battery. 50 years ago when I worked
    on Pilot’s emergency radios and their batteries, I load tested batteries for a specific period of time and then checked the voltages. Low batteries were replaced. We would not want our nation’s defenders out flying around without good emergency equipment.
    I have not had a problem with Kirkland batteries leaking. Many years ago I lived in Portland and I had a source of no cad batteries from
    a warranty repair shop I discovered that those dead C cells in power packs often came back to life if zapped with a jumper cable hooked up
    to a 12 volt battery. It was also almost like an instant charge. Batteries that would not charge in a charger often worked perfect after one or more zaps with a jumper cable hooked up to a 12 volt car battery. Even now I gather recycled batteries from recycle bins and
    recharge them and it has given me many spares for my power tools for free. Ones that do not recharge get an x marked on them and I return them to the recycle box. Free is a very good price for an old man living on Social Security $$$.

  28. I read your article several times. I have two grandsons who go thru batteries over and over. Like you I had a bunch of old dead ones lying around. I decided to try both the Maximal Power FC999 charger and the meter / tester. I had them shipped to me at work. I wanted to test it out. We have a bucket or pail that is full of old dead batteries of all sizes for proper disposal. I picked out 4 AA’s dead by meter test and charged them until they showed OK. Checked them again with the meter. They now show high end of good on the meter. I also found when testing for others to charge there were a lot of batteries that showed good on the meter. And OK in the charger. I have 20 AA that I took home and gave a friend 20 AA’s also. Still charging as I type this. The charger and meter won’t take long to pay for itself at this rate. I keep mining the bucket for AAA, AA, C, and D’s good and those needing charged. The charger only showed 1 battery as BAD so it went back in the bucket. Long story short. Thank you for not only useful information but $$$ savings too.

  29. If they would make one of these a solar unit I would buy one. I think that solar is the only way to go. The sun is always there but the grid probably won’t be.

  30. I used a charger that’s suppose to self adjust to the type of battery. Well I had put in two regular batteries one charges so I took it out added another. The other two were almost charged than bam one exploded. I unplugged it fast as I could and cleaned it up after it sat a few. I wont bother doing that again.

    • The Maximal Power charger requires that you move a switch to indicate the battery type (alkaline or rechargeable for example).

      What an awful experience for you. What brand of charger were you using? I was planning to test other brands and want to stay away from any that are problematic.

  31. I have a Battery Master CL 444 battery charger but I lost the power supply module. Do you know what the power requirements are and if so is the center pin + or – ? I searched the internet but was unable to find any information.

  32. An addition for any who may be interested.

    As you’ll probably have heard the ecig fashion has caused some interest in charging high demand rechargeable batteries. Charging such high-capacity cells could be ‘problematic’ and so there are now ‘charging bags’ available (bags that you enclose your charger in which protects against unwanted ‘side effects’ should the battery vent or explode (they’re available via Amazon of course).

    As capacities of even normal rechargeable batteries increases (I recently purchased some AA’s with a rated capacity of 3200 mAh) it’s always better to be safe than sorry, no? And when mitigating that minor risk is so cheap …

    As an aside, I’ve tried multiple chargers powered via a hand-crank generators (rated at both 1W and 2W output) and all appeared to function fine (solar isn’t really an option in the ‘it’s permanently raining here’ UK), although it’s a ‘lot’ of effort over an extended period (I do ten minutes on, ten off, as and when I can when ‘in the field’). And now trying with normal Alkalines too.

  33. Gaye,

    I recently bought one of the Maximal 999 chargers specifically because of its capability to charge alkaline batteries. WOW. With 3 grandkids (plus our own devices) we really eat AA and AAA batteries. We have already been saving some on recharging the alkaline batteries. It even charged an old alkaline I found in a desk drawer that has been discharged for at least 3 years. It charged it up. It does not hold a good charge but that is the battery, not the charger. The alkalines are not as strong as when they were fresh (probably 60%-80% depending on the battery), but for most uses, it is cheaper to recharge an alkaline than buy new ones. Thanks for the recommendation and evaluation.

  34. Interesting and potentially useful blog post. Here is the truth about the process you are promoting here. Non-rechargable batteries are exactly that, non-recgargable. They produce electrical current by a non-reversable chemical reaction. You and others are simply and absolutely not “recharging” them. Your 9th grade chemistry should have passed along the concept that heat is capable of driving, or accelerating a chemical reaction. The “chargers” being employed are merely warming the non-rechargable cells by passing an electrical current through them and driving the last available limited bits of chemical reactants into the one-way, power producing equation. This uses by far more electrical energy that is available in what little chemical is left. This is also why the warming method posted by Mr. Peter Hughes on 5/3/15 works. It is a good technique to remember when nothing else is available, but you run the serious risk of fire, poisoning, chemical burns and destruction of precious electronics or electrical devices as a result. Please use caution, or better yet be prepared with the better alternatives to this risky process.

    • Um…No….completely and utterly wrong. I have recharged these alkalines that you say “cannot be recharged”, and stored them fro months…and still fully charged…. Please, before you go passing yourself off as some kind of “know it all” at least have some reasonable idea about that of which you are speaking. This segment came directly from WIKI…”…As an alkaline battery is discharged, chemicals inside the battery react to create an electric current. However, once the chemicals have reached chemical equilibrium, the reaction stops, and the battery is depleted. By driving a current through the battery in the reverse direction, the equilibrium can be shifted back towards the original reactants. . My point has been made…

  35. Not to do with recharging, but just a suggestion for those of you who are prepper types. I did a 9 month wilderness experiment a couple of years ago and made the mistake of not packing enough AA batteries for my radio, I had plenty of AAA batteries, but AA’s were all gone, I found that by placing an AAA battery negative post down inside a .45 Colt cartridge it makes the AAA fit perfectly inside the battery compartment of the AA powered radio.

  36. Whoa! I think you read the instruction booklet incorrectly or they printed it wrong:

    Rechargeable batteries should be fully drained before charging, NOT ALKALINES!

    Once an alkaline is drained too much, it can never be recharged. You want to recharge alkalines BEFORE they start to show signs of getting weak. In fact, if you charge them regularly, you can get 100+ charges on them.

    As soon as your flashlight dims at all, put the batteries back in the charger and they’ll last for a long long time.

  37. Love this idea. My son’s wireless Xbox controller eats batteries like a hungry hungry hippo. I posted your blog on my timeline and I am considering a post in my own comedy blog about DIY and helpful websites. If I do create that post, I will likely mention this article there as well. Great article and thanks for the WONDERFUL help. I’ll be purchasing the materials to recharge my old batteries today.

  38. I’m totally on board about recharging alkalines. The problem with recharging regular alkalines is they overheat. I use a basic Batteries Plus Nuon branded recharger and a wind-up kitchen timer. Load the charger, set the timer for an hour, plug in the charger, the timer rings, unplug the charger. Repeat when convenient a few hours later when the batteries are room temperature.

    I also use a voltmeter to tell what the real voltage is.

    Eventually I use old batteries in battery clocks, particularly the oldest NiCad / NiMh. It’s normal to get a year out of a charge in a battery that is dead for any other use.

    The same thing goes for mice and TV type remote controls. I didn’t read 100% of your article but I did see “mouse” mentioned, so I apologize if I covered a subject twice. Then again it’s like confirming your information.

    Your subscription pop-up was interesting because it accessed my browser’s SQLite database to populate an email address selection menu. It makes me wonder how intrusive your website is without letting anyone know. Kind of bad form for a prepper.

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