The Basement Watchdog Big Standby Battery is compatible with all Basement Watchdog battery backup sump pump systems. It is uniquely constructed with heavy duty plates to store more energy, provide longer run times and last longer in standby operation. The high reserve capacity of the Big Standby Battery can run any Basement Watchdog battery backup system intermittently for days. They are shipped dry and vacuumed sealed to retain freshness. Activation is easily started by adding the 6 Qt. battery fluid pack (sold separately). Basement Watchdog Standby Batteries will accommodate the fluid sensor that will allow the battery backup controller to sound an alarm when distilled water is needed.