HK wrote:

I have an old favourite Makita 6v cordless drill/driver that is no longer
taking a charge. The batteries are of the semi-permanent NiCd variety. I
can't find a replacement for them so I was thinking of making my own battery
pack out of AA rechargeable batteries. Easy enough to solder together 4
AAs.

The question is, can I use NiMH batteries instead of the original NiCd?

Absolutly.

If
I do, will the original AC charger work to charge up the NiMHs?

If the charger is not designed for NiMH then it will not work. However,
chargers are cheap so you can get one.



I'm not
sure how the two battery types differ in terms of charging needs.

I'm not sure of the exact difference but they are different.