Battery Question Ni-CD to Ni-MH (Power Tool)

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I have a 4.8V power screw driver that has a dead/weak battery pack and I want to replace the batteries with new ones (All I have on hand is NI-MH batteries) and I was wondering if I can replace the 4x 1.2V AA 600Mah NI-CD with 4x AA 1.2V 1250Mah batteries.

The screw driver is charged by a dc wall adapter 6VDC @ 140MA
I do have an excess of power supplies so finding a proper one should the NI-MH batteries require a different power supply should be fine

Also the power screw driver in question is a Stanley model 63-048
The charger circuit looks to be a dumb circuit also (The manual said charge for 12 Hours after each use and unplug)

Thanks

 

[Mohonri]

Funny you should mention that--my neighbor recently gifted me a 12V cordless drill with bad NiCD battery packs, so I've done a bit of research.

While NiMH and NiCd cells have similar nominal voltages, the charging method is slightly different for each. NiCd cells can be charged simply with a dumb charger--slap 6V (or 5V, or whatever) across it and you're good. NiMH cells, however, can be overcharged if you do the same thing--they heat up once they've reached capacity. All that being said, you *might* be ok with a straight-up replacement, but with your charger being "dumb", I wouldn't count on it.

You have a couple options here. One is to use NiMH cells, and charge them in a separate battery charger. The other option is to buy new NiCD cells, which, despite their toxic contents, can still be readily purchased.

Or you could go all-out, buy some LiIon AA cells, and rewire the battery compartment to 2P2S, and charge the batteries in an external charger.

EDIT: Actually, you *may* be ok with using the NiCd charger, since it appears to be a trickle charger (based on the "charge for 12 hours" thing) : wiki