UKH

Winter is coming and the nights are drawing in. Which battery technologies cope with sub zero temperatures best? I've done a bit of cursory googling and all I've found so far are manufacturers telling me I should buy their most expensive products.

I'm most interested in the comparison between Li-Ion, NiCd and non-rechargable alkaline cells, given that those are the realistic options for headtorches.

I have found the best to be the spare batteries in your pocket )

Smartarse

My Petzl Myo XP has never failed me on winter expeditions, normally lasting a considerable part of the trip before needing new batteries. Sometimes being used in conditions under -30C, taking non-rechargeable alkaline. 

Never used a rechargeable head torch though. 

These batteries have the advantage of being warm.

Warm batteries outperform cold ones, hence separate battery packs on a long cable on some winter/arctic headtorches.

Petzl used to make one like that back in the day with a long cable to battery box, a variation of the Duo. On eBay.co.uk right *now* there's one for sale for £11  (search Petzl Duo) but you'll need to repair it (probably swap twist switch for a mini toggle switch??) and put in a custom duo led module instead of the bulb http://www.customduo.co.uk/Customduo-Modules/ the simple is £25 and is just a push fit into the bulb holder, you'd have a great torch if you fancy a little project to work on

If you're talking about UK use I don't think it's cold enough to make much difference.

Of the ones you've mentioned, they're pretty much all the same - capacity plummets around zero. Bear in mind though that this is the battery internal temperature, not ambient. Alkalines in particular are based on an aqueous electrolyte, so below freezing they're not just struggling to deliver, but also probably getting degraded (how much depends on the precise type).

The only common battery chemistry which has significantly better low temperature performance is Lithium (non-rechargeable, as opposed to Li-ion and its cousins). Something like CR123 3V types. I think these are specced down to -40C.

The simplest answer is use Li-ion and assume they have only 60% of their room temperature capacity. Keep it warm if not in use and NEVER charge it if it's cold (e.g., subzero, warm it up first).