Lithium batteries generate better power below 20 F. Carry batteries in zip-loc bags next to body to stay warm. Electronic accessories are not tolerant of cold. Keep'm warm or leave'm behind. Small iron oxide heating packets can be taped battery compartment Do not rapid fire flash units.
Cold weather zaps the batteries intinally.
Rapid firing before the capacitors are fully recharged will shorten the battery life even further. Optional remote battery packs can help but are expensive. Lens Fogging Set the lens in the sun to facilitate fog reduction. When bringing a cold camera inside, have it in a zip-loc bag with the air removed. The moisture will condense on the outside of the bag.