Sump Pump Repair and Installation
Sump pump battery backup
Short answer
A backup sump pump keeps a basement dry when the main pump fails or the power goes out, which often happens during the same storms that fill the pit. Battery backups run a second pump from a charged battery; water-powered backups use city water pressure and need no power. A plumber sizes the backup to the pit's inflow and installs it with its own check valve and alarm.
Updated · Prepared by the Plumb Right Now editorial team
Sump Pump Battery Backup at a glance
- Why it matters
- Storms that fill the pit often knock out power to the main pump.
- Battery backup
- A second pump on a charged battery; runs for a limited time per charge.
- Water-powered backup
- Uses municipal water pressure; needs no power, but not suited to well water.
- Maintenance
- Test monthly in wet season; replace the battery on the maker's schedule.
Battery vs. water-powered backups
| Battery backup | Water-powered backup | |
|---|---|---|
| Power source | Deep-cycle battery, kept charged | Municipal water pressure |
| Runs during outage | Until the battery drains | As long as water pressure holds |
| Works with a private well | Yes | No, a well pump needs power too |
| Ongoing upkeep | Battery checks and replacement | Annual test; backflow device where required |
| Water use | None | Uses city water to pump water out |
Water-powered units connect to the drinking water supply, so local code typically requires an approved backflow preventer; see backflow testing.
Sizing a backup pump
A backup should keep up with the pit during the wettest conditions you've seen, not just a light rain. A plumber looks at how quickly the pit refills, how high the water must be lifted to the discharge, and how long outages typically last. Battery capacity decides how many hours the backup can run; a larger or second battery extends that.
Combination units pair a primary pump and a battery backup on one controller with an alarm. They save space in a small pit and report problems with either pump.
What installation involves
Check the pit and primary pump
A tired primary pump should be replaced first; a backup isn't meant to run every day.
Mount the backup
The backup pump sits above the primary so it only runs when the water rises past the primary's range.
Separate check valve
Each pump needs a check valve so water isn't pushed back into the pit.
Alarm and charger
A high-water alarm and battery charger with a status light warn you before the basement does.
Keeping the backup ready
- Lift the backup float or use the test button monthly during wet season.
- Check battery terminals and the charger status light.
- Replace the battery on the manufacturer's schedule, often every few years.
- For water-powered units, test once a year and keep the backflow device tested where required.
Related to sump pump battery backup
Common questions
What does the alarm on a backup sump pump mean?
Usually that water has risen above the primary pump's range, the backup is running, or the battery or charger needs attention; check the control panel's status lights.
How long does a battery backup sump pump run?
It depends on the battery size and how often the pump cycles; a busy pit drains a battery faster. Plumbers size the battery to typical outage length.
Battery or water-powered backup: which is better?
Battery units work anywhere; water-powered units run as long as city water pressure holds but don't work with private wells.
Can a backup pump replace my main sump pump?
No. A backup is for emergencies; a primary that runs constantly or is aging should be replaced.
Does a water-powered backup sump pump need a backflow preventer?
Typically yes, because it connects to drinking water; local code sets the requirement.
Can a backup sump pump go in a crawlspace pit?
Often, if the pit is deep enough for both pumps and the discharge line can take a second check valve; combination units help in shallow pits.
How often should a sump pump backup battery be replaced?
Follow the battery maker's schedule; deep-cycle batteries commonly last a few years.
Where does a backup sump pump discharge?
Usually into the same discharge line through its own check valve, or a separate line where the layout calls for one.
Can I add a backup to my existing sump pit?
Usually, if the pit has room; combination units fit smaller pits.
Will a generator replace a battery backup?
A generator can run the main pump during an outage, but it doesn't help if the main pump itself fails.