Yes, many rechargeable batteries have different voltages. They may say 1.25 volts, but that is only an average. I test and computer cycle tons of batteries, and the voltage variance is considerable. Also, NIMH batteries will drop slightly in voltage after a few charges. They will typically level off after that, but they will basically continually get lower and lower on the voltage after multiple recharges. I have seen many NIMH batteries barely make a full vol, and others top out at nearly 1.35 volts. Considering the mass production techniques are pretty lousy, this variance is to be expected.