Tony Hwang wrote in message ...

But charging circuits are different.

Yes.

You can't charge NiMh in NiCad charger or vice versa.

No. You can do it; you just have to monitor current. Of course, it is much
easier and more practical to stick with separate chargers or to purchase one
"smart" charger which you can quickly connect into any battery cradle. Heck,
you can charge just about any cells or battery packs up to 12 volts with a toy
train transformer & a capacitor if you know what you are doing.