One Way To Recharge Alkaline Batteries

It says it right on the side of every alkaline battery – do not attempt to recharge. By which of course the manufacturer means don’t try to force electrons back into the cell. But [Cody] figured he could work around that safety warning chemically, by replacing the guts of an alkaline dry cell.

The batteries in question were certainly old, gnarly looking, and pretty dead – [Cody] barely got a reading on his multimeter. As you can see after the break, he cleaned off the exterior corrosion and did a quick teardown of the dry cells, removing the remains of the zinc anode, now in the form of zinc oxide paste looking very much like what you’d slather on your nose before a day at the beach. He filled the resulting cavity with a putty of zinc dust, freshened up the electrolyte charge with a squirt of 20% potassium hydroxide, sealed up the cell with a little silicone caulking, and put the recycled cell to the test. Result: 1.27 volts. Not too shabby.

[Cody] remarked that he “probably did something wrong” since he wasn’t getting the full 1.5 volts out of his cell; we suspect that since he only renewed the zinc anode and left the manganese oxide cathode alone, he’s only getting the juice out of the half reaction of the zinc side of the electrochemical equation, which has a potential of 1.28V.

A neat hack, to be sure, but it couldn’t possibly make economic sense, right? Not so fast. The zinc dust he used goes for about $30USD a pound, and KOH is about that price for either a 5 pound bucket or a one gallon jug of 45% solution. That would renew the anodes of a LOT of D-sized cells. Even if you added in another $30USD for 500g of manganese oxide, you might still come out ahead of the game. Either way, it’s a good hack to file away if you ever need to MacGyver your way out of a bind.

If you haven’t had enough of the insides of batteries, we’ve looked at tear-downs to get at the dry cells inside. We’ve also discussed the alkaline battery bounce test. And [Cody] has some other useful non-battery tips that we’ve covered before, like his urine-fueled anti-Gorn gunpowder.

[Thanks Hertne]

25 thoughts on “One Way To Recharge Alkaline Batteries

  1. Elektor electronics magazine had a circuit for charging alkaline batteries (I think it used pulse charging) that I built and used successfully a long time ago to recharge AA batteries. Some batteries were possible to charge a few times, some were not. Some batteries developed a leak during charging, so that’s probably the most annoying thing with trying to recharge alkalines. But it is possible.

  2. In the UK about a decade ago, you used to be able to buy a charger unit specifically for this. Commercial item, marketed by many companies, I recall Eveready being one of them. They seemed to disappear about teh same time as NiMH can out and NiCad got cheaper.

    1. We had those on this side of the pond as well. Though still alkaline batteries, the physical construction and chemistry used in the cells were different from most off the shelf alkaline batteries. The cells also had a small amount of the side of the can exposed where a typical alkaline cell would be insulated, and the charger was designed to contact there instead of the end to prevent charging a cell that wasn’t designed to be recharged.

    2. There have been a few attempts to market rechargeable alkaline cells over the years, or to market chargers for standard alkaline cells. The first I remember, in the ’70s, had a theoretical cycle life of 50 or so charges, but didn’t work out well in practice.
      Later, in the ’90s, they were reintroduced with better control of the charging, but still didn’t work out well.

      Now that we have NiMh cells that hold a charge for a year or more, I don’t see the point in recharging alkaline cells.

      On the other hand, taking one apart and rebuilding it is a true hack.

    3. About 20 years ago, I bought a used SuperCharger at the Salvation Army thrift store for $0.25.
      It will individually recharge 4 alkaline or NiCd batteries (AAA to D size) (switch selectable).
      AIUI, The device dropped out of popularity, because it was too conservative in the re-charge, too little, too long.
      The makers probably did it that way to reduce the possibility of over doing the recharge and having lawyers pounding on their door.

  3. BuddyL I think I need to find to do a tear down. Did four battery’s at a time, had three led’s for status, done, charging, and bad. A Ronco product maybe? My experience made the battery’s leak more often…

    later

  4. I’v taken power supplies to alkaline batteries with mixed success, they tend to charge to about 80% of their origional capacity (Wh), however they usually start leaking after being charged. Charging a 9V at the wrong current resulted in a shop covered in bits of 9V battery. :)

  5. If you made one battery out of that, how many Amp Hours would you get for that $90 ?
    … snip …
    zinc dust he used goes for about $30USD a pound,
    and KOH is about that price for either a 5 pound bucket or a one gallon jug of 45% solution.
    Even if you added in another $30USD for 500g of manganese oxide
    … snip …

    1. You can calculate the amount of capacity by figuring the numbers of mols that a pound of zinc is, then the amount of electrons transfer due to the oxidation and the charges involved. Probably a good exam question for high school chemistry.

  6. Or you could just go get 4th gen panasonic/eneloop batteries(the best there is) in C size for like 20 bucks good for 2.1k charges and 3k mah

    I will say this: Batteries aren’t recycled near enough

  7. Rayovac Renewal was the latest commercial attempt at rechargeable alkalines. They had two versions of the charger for four AA cells. The first one only worked with Renewal cells. The second would do Renewal, NiCd and NiMH, AA or AAA and charges each cell individually.

    The first version charger is pretty much worthless for anything. The second version is much sought after due to the individual cell charging which is great for things that take three cells like many LED flashlights.

  8. Neat!

    Forgive me for my ignorance of chemistry, but how would one go about de-oxidizing (or whatever the correct term is) the zinc oxide, and how energy intensive is the process relative to oxidizing? And I suppose you want to do the opposite for the manganese, so my question above also pertains to that as well.

    To put it another way, how does one change the chemistry of the old cell’s contents, and what is the ratio of input energy required for the process to the output you would get from the refreshed cell?

    I guess I’m curious about whether the process involves heat, and if so, then if thermal energy could directly be produced by solar heating and, neglecting the mechanical requirements of repacking the electrolytes (the stuff plants crave – heh), if the process could produce energy more efficiently than that of common solid state solar cells.

    1. The correct term would be “reduction”, and to do that to ZnO you’d need to heat it in the presence of carbon to over 907°C, then catch the Zinc vapor and cool it down

    2. Even besides seeing Mr Drake’s post, I know that producing batteries is horribly inefficient energy wise, takes much more to refine the metals etc, than you ever get from the battery. If you’ve got heat, use it in an engine.

  9. All I’m thinking is “put all this stuff into one container, see how long it lasts. Or rather, how long will a flashlight run on that $30 dollar bag and 5 dollars of 45% solution?

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