I bought some rechargeable AA's and when I went to recharge them I saw that they are alkaline and neither NiCad nor metal hydride, which are the options my recharger gives.

I phoned Radio Shack (from whom I bought the recharger) and they told me that if I try to recharge these alkaline batteries in their recharger, the batteries could explode and also damage the recharger.

Funny thing is, I seem to remember I recharged two of these same alkaline batteries once before: I had not then noticed they were alkaline. But I'm not dead certain.

What's the real scoop?

From BatteryUniversity.com:

quote:

The idea of recharging alkaline batteries is not new. Although not endorsed by manufacturers, ordinary alkaline batteries have been recharged in households for many years. Recharging these batteries is only effective, however, if the cells have been discharged to less than 50% of their total capacity. The number of recharges depends solely on the depth of discharge and is limited to a few cycles at best. With each recharge, the amount of capacity the cell can hold is reduced. There is a cautionary advisory. Charging ordinary alkaline batteries may generate hydrogen gas, which can lead to explosion.

Thank you, perfesser. I looked at a site that discussed recharging alkalines before I posted, and it seemed to suggest it was a 'bad thing'. Probably this was because of the risk of explosion.

I wonder which recharger option I ought to use, NiCad or MH? Actually I could do it outdoors, and experiment. The recharger was cheap, and I'm a fanatical waste-avoider. Disposable batteries drive me nuts.

I have e-mailed Cadex, the company that wrote the article that you quoted, to see if they sell alkaline chargers direct. (In the small town where I live, I couldn't find any -- just NiCad / NiMH chargers.) The e-mail failed. I hate it when that happens.

quote:

I wonder which recharger option I ought to use, NiCad or MH?

Neither! Ni-CD (Nickel Cadmium) and Ni-Mh (Nickle Metal Hydride) carry a 1.2 voltage where as Alkaline carries a 1.5 voltage and should only be recharged by a charger specifically made for rechargeable alkaline batteries. Rayovac PS1 or PS3 are recommended, as well as Pure Energy EnviroCharger or AccuManager Battery Charger.

Thank you, Georgia. Guess I'll try mail order (Sears). Sigh!!!

Just in case anyone else wondered about this problem of alkaline rechargeables, I got this reply from the sponsor of the site Professor quoted from above.

"The reusable alkaline has a different full charge detection to that of NiCd and NiMH. Charging is not recommended. If you need to charge, only do so for a short time and check the temperature. Do not leave unattended.
Cadex Electronics Inc. "

I have since bought an alkaline charger. Note that it warns that it does not work for all rechargeable alkalines, only its own brand. Also, alkalines don't have as long a life.

All in all, it looks as if NiCad and NiMH are the most efficient in money. I don't know which are most harmful environmentally -- likely the heavy metal ones.

Can't just about any battery be at least partly recharged for a temporary period after its first discharge? And by temporary, I don't mean "before it explodes" .

What ever happened to ordinary carbon-zinc cells? Am I showing my age? I heard they were better suited for trickle charging than alkalines, such as the 9 v backup batteries often used in line-powered alarm clocks.

Prof says: "Can't just about any battery be at least partly recharged for a temporary period after its first discharge?"

I guess it can. I recharged some alkalines inadvertently using a NiCad/NiMH charger, and it worked. I must have just plugged them into the recharger without checking. I had shopped for 'rechargeable' batteries, and had not noticed that they were alkaline. I didn't realize I'd done anything 'wrong' until time to recharge, when I went to check for NiCad or NiMH and noticed that the batteries were neither. The options on the charger, NiCad or NiMH, did not include alkaline.

Then I read my alkaline batteries package notes, and found I needed an alkaline charger. Of course I was ticked off, because I had bought a NiCad/NiMH charger and had no need of an alkaline charger except -- I had bought some alkaline rechargeable batteries. It seemed silly to throw away rechargeables after having paid more for them than for disposables.

It's complicated. It seems alkalines have been recharged for years, but that there is some danger of explosion due to gas buildup. If one does attempt it, one ought to moniter the recharging process. The way to prevent gas buildup is to use mercury as a component but it's bad for the environment.

I suppose it's like engine oil. If you live in the south, you can use one grade all year round. But if you live in the north, you may get away with not changing your oil; but you ought to get a lighter grade in the colder weather, or you risk that your engine will seize up. Of course if you really understand the relationship between temperature and oil viscosity, you can fine-tune and get away with it: just don't drive when the temperature is below the critical point.

So what I infer is that you can buy alkaline chargers but the alkaline batteries have a short usage life even if rechargeable; and most are not rechargeable.

If you recharge alkaline rechargeables (as I have ignorantly done) using a NiCad or NiMH charger you risk explosion. See Georgia's post: the voltage is different.