A rechargeable battery used to power burglar and Fire alarms in the event of mains power failure. All systems should be fitted with a battery of suitable capacity, which should maintain the system in a quiescent (non-alarm) state for at least 8 hours. For example a burglar alarm system comprising a Control Panel (70mA) 8 x PIRs (15mA x 8 = 120mA) and an external Sounder (30mA) uses a total power of 220mA, thus a 12v battery rated at 2.1Ah will maintain the system for 9.5 hours if the battery is in perfect condition. Batteries remain in reasonable condition for up to 3 years but they should be checked annually (voltage should be 13v - 13.6v)