One [Jebao] battery backup will power an RW-4 for up to 48 hours, and RW-8 for up to 24 hours, and RW-15 for up to 18 hours, or an RW-20 for up to 12 hours. They can also be daisy chained for more run time or more pumps. The batteries are continually charged while the power is on, and if the power is out, the battery will automatically switch on and power the pumps until power is restored.