Anyone got some insight on batteries? Mainly for headlamp/flashlight/possible GPS ussage.

I know lithium are the only reliable ones for cold weather, they are also lighter and last longer than other types - however are a little more expensive.

I bought some NiMH rechargables today (energizer e^2), not sure if I want to keep them or not as I've never packed with rechargables. I usually just buy a big package of standard alkalines. Probably better environmental wise for the rechargables, but I am concerned with performance. I"ve read rechargables do not put out the voltage as lith/alka so lights may not be as bright (like .5ish volt difference?).

I'm fairly sure lithium would be best weight/performance, but at a price ($). What does everyone use?