This is the standard alarm panel backup battery that we specify. DSC has a minimum recommendation of the 4 Amp Hour battery, the RB412. But the one thing you don't want to do on an alarm panel is drain the battery to zero. Every time you do that the life of the battery is cut in half, and when the power is restored to the panel, the power supply has to do dual duty, charge the battery and run the panel. This action can take out you allarm panel power supply. If you are connecting a full complement of motions and sirens then this is the battery to specify. About 3.3.6 inches and will fit in the standard alarm panel can