Charging NiMH batteries using NiCd charger?

As I've said before on here, NiMh is basically the "new" NiCd technology for rechargeable batteries. You can use any consumer charger for either NiCd or NiMh batteries. The circuitry of the charger is simple and generic. It delivers the same amount of voltage for the same voltage of battery. There is no feedback or sensing circuitry or function. And the battery will determine what current is required, which will be in the same range for either type, all WELL within the design of the charger.

As an electrical engineer for nearly 40 years, I'm telling you that you can use your charger without worry. The only concern for higher rated batteries (mAh) is that it takes a little longer to charge them. It has nothing at all to do with charging current.

Charge Nimh With Nicd Charger

The problem is that NiMH batteries do not tolerate overcharging as well as NiCd batteries.

I assume that the BQ-4C is just a "dumb" charger that will charge the batteries at 240mA forever. This is not too much of a problem if you always completely discharge the NiMH batteries and are diligent about taking them out of the charger after 14 hours or so.

But if you make a habit of leaving them in the charger for extended lengths of time, they will not last nearly as many cycles.

Some cheap (not the best!) NiNH chargers are like your old one except that they use a timer to limit charge time.

If you make a habit of charging mixed NiMH batteries with unknown charge states, you can help the batteries out by discharging them prior to recharging. Discharging NiMH batteries to zero volts is not good for them either, but you can discharge them through a 14001 type diode in series with a 2 or 3 ohm resistor. That way they will stop discharging at about 0.7 volts.

Nope, they have different charging principles and cut-off mechanisms, you risk destroying the batteries. Only a NiCd compatible charger can be used for those batteries.

Only if you want to blow them up.