In article .com,
wrote:

| The main complication would be very short battery life.

As you hinted at, that depends on the charger.

Most cheap rechargable appliances have a slow charger that charge the
battery at around C/10. If you replace 600 mAh AA NiCds with 2400 mAh
AA NiMH cells, the charger will work just fine, except that it's now
charging at a C/40 rate -- which is slow enough that the incresaed
self discharge of the NiMH cells will become an issue, but it'll
probably work just fine. (It might not ever fully charge the
batteries though. But it should be OK anyways.)

You really only have to worry about the charger if it 1) only charges
for X hours, which would mean that it won't fully charge the new,
larger battery unless you unplug it and plug it back in after X hours,
or 2) is a fast peak-detecting charger, as NiMH cells have a similar
peak to NiCds, but it's smaller.

In my experience, most cheap devices that have NiCd or NiMH cells have
slow chargers that will work fine with either. Only the higher
quality ones have things that actually detect when the battery is
actually fully charged -- things like better power tools and the like.
(And of course, anything with LiPo cells. Overcharging them is bad.
But LiPo cells don't fit within the `NiCd or NiMH' classification I
mentioned earlier.)

--
Doug McLaren,
It's hard to be nostalgic when you can't remember anything. --Unknown