Just to chip in, on my "pre EOS"
A610 the AA rechargeable batteries are still in good shape 3 year on

Mind you they are run on an expensive charger that has some electronics though...
On a side note - AA rechargeable batteries should (if they are powerful) allow for a few more pictures than normal batteries.
(for the
A610 - 1600mAh each rechargeable battery)
If the charge is lost very quickly I'd say its a fault somewhere.
If the batteries get warm then this is a sign that they are discharged quickly.