in the event of a power failure,the back up will power the pump at reduced speed to conserve power,and it is automatic...you can also reprogram the pump to use even less power by slowing it down even more during an outage...
nice addition to the Vortech pumps,and although they're a little pricey,it's really cheap insurance for your tank...it'll more than pay for itself the very first time you don't lose over a $1000 worth of livestock to a power outage :D