Probably once or twice a year lately... Generally during a storm, and when we get knoked out from a storm it's been anywhere from 6 hours to 6 days. It's nice to be able to heat the house and run the sump pump, watch TV, get online (if available), and keep the fridge running. BTW I also rigged my sump pump with a backup 4000 GPH 12v bilge pump on a deep-cycle battery on a trickle charger. It's set to trigger at a higher water level than the AC powered one.