And a Battery University link: http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures http://batteryuniversity.com/learn/article/di

And a Battery University link: http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures http://batteryuniversity.com/learn/article/discharging_at_hi... And the most relevant paragraph: The performance of all battery chemistries drops drastically at low temperatures. At –20°C (–4°F) most nickel-, lead- and lithium-based batteries stop functioning. Although NiCd can go down to –40°C (-40°F), the permissible discharge is only 0.2C (5-hour rate). Specially built Li- ion brings the operating temperature down to –40°C, but only on discharge and at a reduced discharge. With lead acid we have 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.