Taken from battery university.
Like humans, batteries function best at room temperature. Warming a dying battery in a mobile phone or flashlight in our jeans might provide additional runtime due to improved electrochemical reaction. This is likely also the reason why manufacturers prefer to specify batteries at a toasty 27°C (80°F). While operating a battery at elevated temperatures will improve performance momentarily, prolonged exposure will shorten life.
As all drivers in cold countries know, a warm battery cranks the car engine better than a cold one. Cold temperature increases the internal resistance and lowers the capacity. A battery that provides 100 percent capacity at 27°C (80°F) will typically deliver only 50 percent at –18°C (0°F). The momentary capacity decrease differs with battery chemistry.
The performance of all batteries drops drastically at low temperatures; however the elevated internal resistance will cause some warming effect. At –20°C (–4°F) most batteries stop functioning. Although NiCd can go down to –40°C (-40°F), the permissible discharge is only 0.2C (5-hour rate), Specialty Li-ion can operate to a temperature of –40°C, but only at a reduced discharge rate; charging at this temperature is out of question. With lead acid there is the danger of the electrolyte freezing, which can crack the enclosure. Lead acid freezes more easily with a low charge when the specific gravity of the electrolyte is more like water than when fully charged.
