Originally Posted by steelbikeguy

Here's the datasheet for the Panasonic AA NiMH.
and one for the Energizer AA NiMH.

For my use in standlights, NiMH doesn't look like a good choice because the manufacturers only provide specs for charging at or above 0C. They are a bit more particular than nicads in terms of continuous charging, but that's not hard to accommodate.

As for discharge characteristics, Panasonic does have specs for temperatures down to -10C. No graphs or info on how much the capacity is reduced, though.
Energizer only specs discharge down to 0C, so I don't know if they are being conservative or if their batteries are less suited for cold than Panasonic. The datasheet does include the admonition "NOTE: Operating at extreme temperatures will significantly impact battery cycle life".

Energizer does provide more generalized info on NiMH batteries in their NiMH Handbook.

In general, all batteries operate by the use of chemical reactions to generate electron flow. Chemical reactions occur slower in cold temperatures than in warm, so it's to be expected that performance will drop when things cool off. Super capacitors offer better performance in the cold (although I haven't checked the datasheet...), but have to be much, much larger to provide an equivalent amount of energy.

Steve in Peoria