The extreme cold temperatures currently covering the United Kingdom are having a deleterious effect on the life of 12v battery supplied electric fencing units. The 12v wet cell batteries being used to run these units are releasing the current at a lower voltage and the stored capacity is reduced by the cold temperatures.
This is caused by the cold affecting the chemical processes. All normal batteries convert chemical energy to electrical energy to enable it to push electrons into the circuit and most of these chemical reactions happen faster and freer at warm temperatures (perhaps between 15c and 37c) so a cold battery won't deliver the current or life of a moderately warm battery. When an increase in temperature occurs the electrons are excited. A decrease in temperature inhibits electron flow. This is a natural reaction on electrons in most systems. Furthermore, the combination of a rapid temperature change and high humidity can cause condensation to form and a potential hazard for your battery and device for that matter.
Cold enough and it won't work at all. The electric current generated by a battery is produced when a connection is made between its positive and negative terminals. When the terminals are connected, a chemical reaction is initiated that generates electrons to supply the current of the battery. Lowering the temperature causes these chemical reactions to proceed more slowly, so if a battery is used at a low temperature then less current is produced than at a higher temperature. As the batteries run down they quickly reach the point where they cannot deliver enough current to keep up with the demand.
Temperature has a pronounced affect on battery life (Recharges and length of use). For every ten degrees of change in room temperature, Up to 50% of its' life is lost. So a battery with a life of a 100 charging cycles is reduced to 50. Usually a cold battery will be fine when thawed again, however a lead-acid or other wet-cell battery could rupture and be destroyed if frozen solid.