Instructables
Picture of Easily recharge alkaline batteries!
Did you know that you can recharge alkaline batteries? Well, they're not perfect (don't have very good recharge capacity, few recharge cycles, etc) but you can recharge them to an extent. Many people have developed fancy charging circuits, but I was able to get charge into some Alkaline batteries with just an old cellphone plug.

The adapter says 3.7V, 300mA. With that sort of current, you shouldn't leave the batteries connected very long at a time. The voltage on the batteries will go up quickly, but the actual amount of charge will not. Because of this, you have to disconnect the batteries frequently to let them "cool down" (though they usually don't even get warm, the voltage will quickly drop down to around 1.5 V after disconnecting). After they have leveled off (usually around 1.5V) put it back on the adapter for another minute or so. Repeat this a bunch of times to get the charge up. I've just started experimenting, but I was able to get enough charge in two completely dead batteries to start up my power-hungry Canon digital camera and take a few pictures (with screen and flash) and turn it off without it dying on me (died the next time I turned it on). With a better circuit, you could automate the on/off cycles to charge them up.
 
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Step 1: Get your power source!

You'll want to find an adapter plug from something you don't care much about. Backwards powering batteries can lead to current backflow (battery power going through adapter) which can ruin some adapters, though usually at 1.5v you're safe (burned out a cheap 5v plug trying to recharge a 9v though). I found a Nokia phone charger works good.

You also don't want really high amperage. Since high current charging leads to leaking batteries, try to find as low current plug as possible (look at the mA rating). A good charger has only 65 mA or so going through the battery, but mine has 300 so that's why I have to keep cycling the power to the battery.
kkelley59 days ago

For several years now I've been recharging my AA and AAA batteries on my Philips Sonicare toothbrush holder. I'm sure any electric toothbrush charger would work. Just place the batteries flat side (-) down and let charge for several hours or overnite. I use a rubberband to hold them together so that they don't roll off. If they still tend to roll then just pack a little paper around them to hold in place.

locofocos6 years ago
I've actually built a power supply to feed it the proper current and voltage (but more the proper current). I followed the instructions on http://www.afrotechmods.com/reallycheap/batteries/batts.htm to build it. For some reason (either I got the wrong kind of transistor or my resistor is bad) it's giving WAAAAAYYYY too much current. I fully charged 2 AA batteries in less that half an hour :P . I guess I'll keep it because I might need to charge some batteries really quickly, but I'm gonna go to radio shack to get some real parts to build it from and maybe even a generic PCB. My advice- be very careful recharging button cell batteries. I tried to recharge some little ones that went in my laser pointer cause radio shack wanted 5 bucks each (3 batteries times 5= 16.50 with tax) and left them on for a little too long.... the one on bottom exploded. And I mean exploded. The other two batteries got shot into the air. I looked at them, and the 2 flat sides were bulging out, about to pop.
I get button cell batteries from the dollar stores, usually Dollar Tree. They are not the highest capacity, but at 1/5 the price or even less, suits me fine. I use them in turkey scopes, lazer toys, bicycle computers, no problems. Look on Fleabay, too, or battery hobby websites. You can buy in bulk.
We used to put those old dead button batteries on the electric stove until the popped. As for your high priced Radio Shack gouging your pocket, go to walmart back in electronics. The 357 button cells are a cross reference battery replacement. Don't go to the jewlry counter, they'll charge just as much to sell you batteries. One jewlry gal told me the 357's in electronics are the same thing. She was right, I've been using them since.
ketan7s2 years ago
Seems like all these 'explode' 'explode' members are the commercial agents or employees or bribees of alkaline battery companies.
So you said "put it back on the adapter for another minute or so". Which means you have to charge the batteries for one minute and turn off every minute??
how many minutes sessions should I do to charge the battery to proper extent?
hansonsux4 years ago
It is generally not a good idea to recharge regular alkaline batteries. The reason being is they produce a lot of gas, and thus frequently end up rupturing the seals. The seal may not fail until days later - after the battery you thought was good and you put it into a device... goes pop! and now you have a mess to clean up.  Even then, the capacity is usually very short, and the internal resistance is very high.
hskfighter4 years ago
i charge the sanyo batteries with a camelion standard charger can it effect the life span of the battery??????
hskfighter4 years ago
i have canon power shot a470 i used rechargable batteries in it.i used sanyo 2700mAh.as battery in it.its life span has decreased to very short when i charge the battery for 16 hours and then i get in the battery the power shot after capturing the image says change the batteries. help!!!!
they just might do something interesting! Like blow up in your face!
xerxesx205 years ago
Could you not use a small series resistor to drop the the voltage down to about 1.6-1.8ish. Also, could you not use a parrallel resistor to dump some current away, simulating a load, not very efficient I know but.. just a thought. Target current of about 200-500ma i'd have thought wouldn't toast anything. This would give a long charge cycle as the voltage isn't to strong, nor is the current so it would be okay-ish to leave them I reckon. What are your thoughts people? Any help much appreciated, I generally have a few of old alkalines around and they are a cinch to get hold of! Root around in your desk drawers, see what turns up!
either that, or only charge sets in parralel, so that the current gets halved through either set.  If one set goes disfunctional, it will source all of the current through the other one though, and probably kill them too.
Ironman974 years ago
I have the same volt meter.
12V5 years ago
i made the circuit and it charged my 9v pp3 to 10v in 3 hours ............ not a single drop of electrolyte leaked out !
12V5 years ago
how many charge cycles do you get(approx average ) and how do you know when they are unchargeable any longer(battery needs to be replaced)
I have to agree with PKM about the potassium hydroxide electrolyte. It is corrosive like acid and will burn you mildly. Not anything you really want on you. It is also commonly used as a root killer in sewer lines and costs about 9 bucks at the hardware store per quart.

Correct me if I am wrong, but a friend in Florida told me switching acid batteries to alkaline gives you 1.5 volts per cell, 15 volt output. My car voltage regulator could withstand 15.5 volts. I never tried it. He said the railroad uses this method to keep batteries self cleaning, greatly extending the life of the battery. The alkaline apparently cleans the sulphate off the plates until the alkaline oxidizes them and won't hold a charge. Then covert back to acid he said. Never tried it though.
tanmanknex5 years ago
just had a thought, but what if you put a resistor instead of a wire in the plug center? if the current is too high, i mean.
to charger aa battery the charger shud be 2vdc. 200.ma or to sun charger the battery shud be 2.5v dc 200ma
its best to recharge alkaline batteries when they are about halfway dead. when they are completely dead they don't like to take a charge for anything.
Hi all, I can remember making an alkaline charger for my A level project. I can't remember all of the details, but it involved Periodic Current Reversal(PCR), whereby a rectifier wasn't used. the whole thing worked by positively charging the batteries more than the discharging. 4.5VAC was used i think and for each of the battery groups(AA,C,D) a circuit comprising of two resistors and one diode - different R's for each group. I think that were even specific lengths of time for each group too! If I can find any docs, I'll post them
CalcProgrammer1 (author) 6 years ago
Finally had a battery "go out" on me! I've been charging 6 AA's in series with a 9V/300mA charger for most of the day (though my ammeter said only about 80-100mA were going through) . I'm sitting here reading stuff online when I hear this popping noise. I run over to the batteries and immediately pull the plug and shutdown, take the batteries out of the holder and set them aside, checking for leaks. Turns out one of them did leak a tiny bit of electrolyte in the holder, but that was easily absorbed with a piece of paper. Nothing dangerous about it, just a little "acid" though it probably wasn't really acidic. I'm letting the batteries "cool down" (they didn't get hot, maybe just a bit warm) and then I'll see if the voltages even out at 1.5V and run stuff.
The stuff inside does seem to be reactive with aluminum though, placed the leaky battery on a sheet of foil and the stuff started bubbling and leaving a green spot. Now I'm interested to see what becomes of this...The rest of the batteries also seem to have overcharged, because they are leaking a bit and when I put them in my camera it wouldn't even fully power up before turning off.
1oooop6 years ago
I agree, I like to take the batteries out when I'm not using, it saves many batteries.
LinuxH4x0r6 years ago
Try using a lower amperage and doing it for longer (I've seen ones up to 24 hrs) Great job!
CalcProgrammer1 (author)  LinuxH4x0r6 years ago
I can't find a lower amperage supply and I don't know how to build one (or have the parts probably) so I'm just doing it this way. Lower amperage is better though.
Trans_Am6 years ago
Alkaline batteries don't "explode" per say, it's more like "pop". I had some cheapo rechargeable alkaline batteries (yes, rechargeable) and they weren't holding charge anymore, so I just used this method with a higher voltage. 12V 1A adapter into a 1.5V battery. It worked a couple times, but on the last cycle, the battery overheated and "popped".
The trick is way higher voltage but barely any current...
flactemnad6 years ago
I used to charge alkalines in a regular battery charger. I experimented and knew how long to charge them without getting hot or over voltage. Would I recommend anyone else do it? No way - they are prone to explosion when being charged. I don't do it anymore for just that reason.
I used to do that too, and right on the charger it said "explode" right on there. But I never really knew what level that meant. Is it like a giant fireball that can be seen from space and leaves a huge smoking crater where your house used to be, or simply the case splitting open and letting a little toxic crud out? To what extent does it "explode"?
CalcProgrammer1 (author)  PS1186 years ago
Pretty sure it means the latter...if you're expecting battery fireworks or expecting to use it as a deadly weapon, good luck with that...the worst I've seen (and it wasn't even charging!) was an alkaline AA popping open and leaking some "acid" out onto the living room table (it burned a little mark into the table, but other than that, it was harmless).
CalcProgrammer1 (author)  flactemnad6 years ago
A NiCd or NiMH charger? I'd think that it'd be OK to use a NiCd charger as those usually put out much less power than NiMH chargers do. Especially 15 minute chargers, my NiMH charger has like a 4 Amp adapter, so that could translate into 1A per battery (though it has to run the internals and a cooling fan). It's pretty safe to charge Alkalines but you have to keep a close eye on them (temperature, voltage, etc). As long as you monitor them I don't think you'll have problems. Also, I doubt "explosion" actually means like a giant fireball, I've had a cheap Alkaline AA "blow up" even though it had never been recharged. It was just sitting there and then the end cap blew off and sent acid over our wood table. That left a mark. I think it'd be safe to experiment in the basement, where there's concrete floor and plenty of room.
trispark6 years ago
I'm in Europe and bought an advanced battery charger (Medion 15 Euro). It can charge 4 batteries individually. It can also charge alkaline batteries. The power ratings show about 500mA for NiMh and 180mA for alkaline. I didn't have much success as I expected. Most batteries didn't charge too well or show as 'bad'. They appear full very quickly but run out in seconds in toys. Some cheaper batteries grow in size, ready to explode! My most successful charge were the batteries in my new Canon camera. Panasonic professional alkaline. They took longer to charge but still drained pretty quick.
CalcProgrammer1 (author)  trispark6 years ago
I've read if you charge them at currents <100mA and you let them charge for a long time (like a day) you can get enough power to almost completely recharge.
PKM6 years ago
Firsly, I believe the "alkaline" bit means they don't contain any battery acid :) "battery acid" is commonly used to mean the sulphuric acid in car batteries, which there definitely isn't in alkaline batteries, but the KOH electrolyte is still nasty stuff that you don't want on your skin, eyes or furniture.

Secondly- your adapter should have a symbol like + ------ o) ----- -, meaning it is plus-tip (positive centre) , or - ------ o) ----- +, meaning it is the other way around (negative centre, positive ring). Excuse my terrible ASCII art :)

A decent wall-wart adapter will often have a switch letting you change the polarity of the plug, but I would expect all sensible power sources to at least have this diagram.
CalcProgrammer1 (author)  PKM6 years ago
You'd be wrong on that one lol...neither one of the two phone chargers I tried had said diagram. Most do, but a lot of new "specific use" plugs that are designed to work only with one thing don't put the diagram on the plug. If you get one from RadioShack, for instance, you can flip the plug around to change polarity, or just stick wires in the adaptaplug socket (the special two pin socket that they use to change tips with).