A backup sump pump has to keep up with the water coming in during the outage or primary-pump failure you’re planning for. Compare backup pumps by their published flow at your actual vertical lift, not by open-flow headline numbers. Then choose the power source: a battery for power outages, or municipal water pressure if your water service and local code allow it.
Battery vs water-powered
| Battery backup | Water-powered backup | |
|---|---|---|
| Works during a power outage | Yes, while the battery lasts | Yes, if municipal water pressure holds |
| Main limit | Battery capacity and condition | Water pressure and flow, plus code approval |
| Homes on a well | Works | Generally not, because the well pump stops |
| Upkeep | Battery checks and replacement, charger status | Backflow device testing, water use |
Battery runtime depends on your setup. Zoeller recommends a deep-cycle 12-volt, 105 amp-hour or larger marine battery for its Aquanot 508. It says that battery gives about 6 hours of continuous pumping with 8 feet of head, and longer when the pump runs intermittently. That figure doesn’t carry over to another pump, battery or lift. Don’t substitute a car starting battery where the maker specifies a deep-cycle battery.
Water-powered units use municipal water pressure to move sump water. They need adequate pressure and flow, an approved backflow preventer, and local-code acceptance.
Check fit as a system
Confirm each of these against the product’s instructions:
- Flow at your lift and discharge length
- Basin size and room for both pumps’ floats to move freely
- Discharge plan: Zoeller’s Aquanot 508 can tee into the primary pump’s discharge, with an in-line check valve on the primary and a built-in check valve on the backup
- Battery type, size and terminals, and the charger’s status lights
- High-water and low-battery alarms, plus any remote-alert terminals
- Freeze protection for the discharge line
Test it under water load
A status light doesn’t prove the pump can move water. Zoeller’s Aquanot 508 instructions call for a test at least every 3 months:
- Unplug the primary pump and the backup’s charger.
- Fill the sump to the backup pump’s “on” level and let it run a few minutes.
- Confirm the alarm sounds shortly after the backup starts, then reset it.
- Plug everything back in and confirm the primary pump returns the pit to normal.
Check that water actually discharges outdoors during the test. For alarm-only checks, see how to test a sump pump alarm .
Related guides
FAQ
How long will a battery backup sump pump run?
It depends on the battery, the lift and how often the pump cycles. Zoeller, for example, says a deep-cycle 12-volt, 105 amp-hour marine battery gives its Aquanot 508 about 6 hours of continuous pumping at 8 feet of head. Intermittent pumping stretches that.
Is battery or water-powered better?
Neither is better everywhere. A battery system needs a compatible, maintained battery and charger. A water-powered system needs reliable municipal pressure, approved backflow protection and local-code acceptance.
What if the home is on a well?
A water-powered backup generally can’t run when the well pump loses power. A battery system, or a generator plan that covers the primary pump, fits better.
How often should I test a backup sump pump?
Follow the manual. Zoeller’s Aquanot 508 instructions say to inspect and test at least every 3 months, by unplugging the primary pump and charger and filling the sump to the backup’s on level.