How Long Will a Power Station Run a Sump Pump?
Estimate sump-pump runtime from pump watts, duty cycle, battery capacity and startup requirements.
Sump pumps are difficult to estimate from running watts alone because they cycle and can have substantial motor startup demand.
Runtime cannot be calculated from pump watts alone because sump pumps cycle. Estimate energy per cycle or average minutes running per hour, then divide usable battery watt-hours by that hourly energy. Also verify inverter surge separately.
What matters
- Measure or estimate duty cycle during actual rain conditions.
- Verify startup surge separately.
- Heavy storms can push duty cycle much higher.
- Recharge access matters in multi-day weather events.
Decision factors that change the answer
Run minutes/hour
A pump running 5 minutes/hour uses half as much energy as the same pump running 10 minutes/hour.
Storm intensity
The duty cycle can increase rapidly as groundwater rises.
Inverter losses
Usable AC energy is lower than battery nameplate capacity.
Motor start
A runtime calculation is irrelevant if the inverter cannot start the pump.
How to size it
- Find pump running watts.
- Estimate percent of time running.
- Calculate average effective load.
- Divide usable battery energy by average load.
An 800W pump running 20% of the time averages 160W before losses, but the inverter must still start the full motor load.
Worked example
A 700W pump running 10 minutes/hour uses about 117Wh/hour. A 2kWh station with 1.7kWh usable AC energy would provide about 14.5 hours at that duty cycle. At 20 minutes/hour, runtime falls to about 7.3 hours.
Common buying mistakes
- Assuming a fixed duty cycle in all storms.
- Ignoring startup surge.
- Sizing from energy only.
Use the runtime matrix for energy duration, then verify the pump’s startup requirement independently.
Check the underlying numbers
Use these site resources to replace generic assumptions with your own load or the source-linked data behind this guide.
Use the numbers before choosing a model
Start with your load list. The battery needs enough watt-hours for the desired runtime and enough continuous/surge watts to operate the appliances at the same time. Then check whether your recharge method can replace the energy you expect to consume.
For outage planning, we recommend keeping reserve capacity instead of designing a system that reaches 0% at the end of the forecasted outage.
Next step
Estimate battery runtime → or Build a critical-load energy budget →.