Having a battery backup sump pump is important. They work by automatically coming on as soon as the main pump stops working or can’t keep up with the rate of water inflow.
The backup isn’t just a battery connected to the main pump—it’s a totally separate pump. Though, you can buy combination sump pumps that have both a primary and a backup pump in the same unit.
Most models of backup pump will run occasionally just to check that they’re still functioning. If they aren’t, they’ll sound an alarm to let you know. If you find that your backup pump (or your main pump for that matter) isn’t working, fix the problem as soon as possible.