1. An apparatus, comprising:first and second input terminals configured to be connected to a charging power source for charging a backup power supply for an emergency lighting system and to receive an input voltage from the charging power source across the first and second input terminals, the input voltage corresponding to an applied nominal operating voltage of the charging power source among a plurality of nominal operating voltages for the emergency lighting system, each nominal operating voltage corresponding to a type of AC mains;
a voltage level detector configured to produce, in response to the received input voltage, an input voltage level signal indicating the applied nominal operating voltage of the charging power source to which the input voltage corresponds;
a temperature detector configured to determine whether a temperature in a vicinity of the backup power supply exceeds a backup power supply temperature threshold and to produce a temperature signal indicating whether the temperature exceeds the backup power supply temperature threshold; and
a heater including a plurality of heating elements configured to be selectively activated to heat the backup power supply,
wherein the temperature signal determines whether the heater is activated, and when the heater is activated the input voltage level signal determines which of the heating elements is/are activated; and
wherein at least one heating element is configured to be selectively activated while another heating element is configured to be selectively deactivated in response to the temperature signal and input voltage level signal.