Battery life

Even modern batteries hate cold weather. Their performance deteriorates significantly in lower ambient temperatures.

Keep battery powered devices protected inside bags or jackets, and always carry spares for 'mission critical' devices (apologies for that phrase, but it does best describe devices such as torches and GPS).

Beware of battery life indicators on devices as well. They actually signify voltage drop, and most batteries maintain a steady output for most of their life and then drop off VERY quickly. A battery showing anything less than full charge may not have much life left in it