Prius = re-usable diapers?

I'm still a skeptic of hybrid cars. Not because of the minimal gas savings (if we were paying European or even CNDN prices, the fuel savings would easily cover the cars' price premium), and not so much because of reliability (although the proof isn't yet in the pudding; these cars just haven't been around long enough).

The main question that I have, which has not to my knowledge even been touched upon let alone addressed in the lay-media is: What is the environmental trade-off of saving gas with a hybrid car?
Using re-usable diapers was an "environmentally correct" alternative to using disposable diapers...until one thinks about it. There is in-fact a trade-off. By using cloth diapers, one lessens the plastic load in landfills but increases the amount of polluted freshwater. There is a (somewhat) similar trade-off when using a hybrid car. One doesn't magically save gas when driving a hybrid. One cost is the large NiMH battery involved. What is the environmental cost of manufacturing/recycling/disposing of this battery? Is this cost equal or less than the cost of burning a few thousand gallons of gasoline?

I'm not anti-hybrid. I'm anti- driving/buying hybrids without a critical look...