What size battery backup does a sump pump need?
About 900 Wh for a day for a 1/2 HP pump that runs 15 seconds six times an hour, plus 3,200 W of surge to start it. Time yours below.
Your pump
Times it runs per hour
Count during heavy rainSeconds per run
How long is the outage
Battery you need for 24 hours
900Wh
Plus at least 3,200 W of surge to start the pump.
- Pump running watts
- 1,050 W
- Run time
- 1.5 min per hour
- Energy used
- 630 Wh
- On a 12 V battery
- 75 Ah
Smallest match in our list
EcoFlow DELTA 3 Plus
1,024 Wh · runs this pump for about 33 h
For a backup that takes over by itself, the unit must stay plugged in and offer automatic switchover (UPS). Check the maker's switchover time.
Power stations that fit
| Model | Battery | Surge | For your pump |
|---|---|---|---|
| EcoFlow DELTA 3 Plus | 1,024 Wh | 3,600 W | Fits · 33 h |
| EcoFlow DELTA 2 Max | 2,048 Wh | 4,800 W | Fits · 66 h |
| Anker SOLIX F3800 | 3,840 Wh | 9,000 W | Fits · 5 days |
| EcoFlow DELTA Pro 3 | 4,096 Wh | 8,000 W | Fits · 6 days |
| Jackery Explorer 1000 v2 | 1,070 Wh | 3,000 W | No · surge too low to start the pump |
| Anker SOLIX C1000 | 1,056 Wh | 2,400 W | No · surge too low to start the pump |
| BLUETTI AC180 | 1,152 Wh | 1,800 W | No · surge too low to start the pump |
| BLUETTI Elite 200 V2 | 2,074 Wh | 2,600 W | No · surge too low to start the pump |
Specs from each maker, checked 2026-10-11. Surge must cover the pump's start, or the unit shuts off.
Time your pump in two minutes
- Wait for steady rain, when the pump cycles often.
- Count how many times it switches on in 10 minutes and multiply by 6.
- Time one run from start to stop.
Use your worst storm, not an average day. That's when the power goes out.
Your options
| Option | Good at | Watch for |
|---|---|---|
| 12 V backup pump with its own battery | Takes over by itself, and covers a failed main pump | Often pumps less than the main pump. Compare gallons per hour. |
| Power station | Runs your existing pump, plus a fridge or lights | Surge rating, and automatic switchover if you're away |
| Generator | Long outages, with refueling | Someone has to start it. Run it outdoors, 20 ft from the house. |
Questions
How big a battery backup do I need for a sump pump?
It depends on how often your pump runs. A 1/2 HP pump that runs 15 seconds six times an hour uses about 630 Wh a day, so you need about 900 Wh of battery after inverter losses and 20% headroom. In heavy rain, at 20 runs an hour, that rises to about 3,000 Wh.
Can a portable power station run a sump pump?
Yes, if its surge rating covers the motor start. A 1/2 HP pump needs about 3,200 W for a moment at start-up and a 1/3 HP pump about 2,400 W. Several 1,000 Wh units list a surge below that and will shut off instead of starting the pump.
How long will a battery run a sump pump?
Divide the usable battery energy by the pump's average draw. A 1,000 Wh battery at 85% efficiency gives about 850 Wh. At the example duty above, that's well over a day. In constant heavy rain it can be well under one.
Will a battery backup switch on by itself when the power goes out?
Only if it's built for it. Dedicated sump backup systems and power stations with automatic switchover (UPS) take over without you. Others need you to plug the pump in. Check the switchover time the maker lists.
Is a 12 V backup pump better than a power station?
A dedicated 12 V backup pump is a second pump with its own float switch, so it also covers a failed main pump. A power station runs your existing pump and doubles as backup for a fridge or lights. Many homes in wet basements use both.
How do I find my sump pump's watts?
Check the label on the motor or the manual for watts, or volts × amps (for example 120 V × 8 A = 960 W). If you only know the horsepower, use the 1/3 HP or 1/2 HP option.
Method and sources
Energy = running watts × run time per hour × outage hours. Battery = energy ÷ 85% inverter efficiency × 1.2 headroom, rounded up to 100 Wh. Surge = running watts + starting watts. Full method.
- Champion Power Equipment, Generator Wattage Chart (1/3 HP and 1/2 HP sump pump watts)
- Power station specs: each maker's product page, linked in the table