3Ah 12V DC Sealed lead Acid Battery. As fire alarm systems are life safety systems, they must have a battery backup in order that they will operate in the event of a mains failure. All parts of the system, including auxiliary power supplies must have a battery backup. All the batteries stocked are 12 Volt batteries, meaning that 2 batteries are required for a 24 volt system. The standard capacities stocked are 3.4Ah, 7.2Ah, 12Ah and 17Ah.