It depends on the size of the battery and the backup sump pump system that is doing the charging.

• The Big Dog system has a powerful 20-Amp smart charger that will charge a discharged battery in approximately 6 hours.
• The Basement Watchdog Special has a smaller 1.6-Amp smart charger and can take up  to 3 days to fully recharge.
• The Emergency system is a small .4 amp trickle charger and can take several days to recharge a battery.

Alternately, you could take the battery to a service station or battery or auto parts store for a quick charge, or hook the battery up to an automotive charger if you have one. Be sure to disconnect the control unit from the battery if you are using an automotive charger. If you don’t, the control unit may be damaged.