subject: Recharge Nimh Batteries In An Old Nicd Charger [print this page] Old NiCd chargers handle only NiCd batteriesOld NiCd chargers handle only NiCd batteries. But most NiMH chargers handle both NiMH and NiCd. So if you have an old charger, you can charge only NiCd. If you have a new charger, you can probably charge either NiCD's or NiMH's.
Some chargers are dumb and just charge for a preset amount of time. As a result they almost always run too short (and don't fill up your batteries all the way) or they run too long and damage the batteries, shortening their useful life, meaning can't be recharged nearly as many times. These things are true even with charging NiCD batteries in a NiCD-only charger. But once you go sticking NiMH's in a NiCD-only charger it gets even worse:
Earlier we advised you not to charge NiMH batteries in an old NiCd-only charger. That hasn't stopped many of you from writing and asking, "Are you sure? Are you sure?" Yes, I'm sure. Don't do it. If you need a further explanation then here it is.
If you put a discharged NiMH battery in a dumb NiCd-only charger then the charger will probably fail to fill up the battery, because NiCD's have a smaller capacity than NiMH's so the charger doesn't run as long as it needs to to fill up the NiMH. It won't hurt the battery, but you won't get a full charge either. In many cases you won't even get half of a full charge.
But what if you accidentally put a charged NiMH battery in a dumb NiCD-only charger? Then the charger charges it anyway, and since the battery is already charged then it gets overcharged, and probably damaged or ruined. It may even start a fire if it gets too hot.
There are also smart chargers which check to see when the battery is full and then stop charging. They can tell when the battery is full because the voltage actually starts to drop when more juice is pumped into an already full battery. The problem is that the voltage drop in a NiMH battery is harder to detect than with a NiCD battery, and most NiCD smart chargers can't detect the NiMH drop, so they keep charging anyway, damaging or ruining the battery, or maybe starting a fire.
You can't tell whether your charger is smart or dumb just by looking at it. Even the manual probably won't tell you, you have to check with the manufacturer. Don't write to me, I didn't make your charger and I don't have any special knowledge about it. You have to check with the manufacturer
