But my experience over the past couple decades has been that they aren't. In particular, I've found that they don't hold a charge for very long and that they leak. The latter issue might be a tad expensive if not caught in time (ie, necessitate the purchase of a new mouse).
Yep, rechargeable battery technology has advanced quite a lot in the last decade or so.
NiCd batteries--the old-fashioned rechargeable batteries--pretty much suck. They have limited capacity, they have limited power (1.2 volts rather than 1.5 volts), they leak, and they store very little charge.
Newer batteries, like NiMH and lithium ion, are a lot better. Lithium ion rechargeables are actually more powerful than disposable alkaline batteries; they last longer than alkalines and can be recharged. Of course, their failure modes tend to be pretty unpleasant, but in applications like rechargeable mice they're unlikely to fail catastrophically.
