Battery Backup for a Well Pump for 24 Hours
Estimate one-day battery storage for a well pump using motor power, expected run time and startup headroom.
Well pumps usually operate intermittently, so daily energy can be moderate even when motor startup power is high.
Well-pump backup must satisfy both 240V/starting-surge requirements and total daily pumping energy. A pump can have modest total runtime but still demand a powerful inverter to start. Measure or estimate gallons/day and pump run time rather than assuming continuous operation.
What matters
- Find pump voltage and running watts.
- Estimate cumulative run time per day.
- Startup surge may require a much larger inverter than average energy suggests.
- Some wells require 240V output.
Decision factors that change the answer
Voltage
Many well pumps are 240V, which immediately narrows compatible backup architectures.
Startup surge
Motor startup can be several times running power.
Daily duty cycle
Energy use depends on how long the pump actually runs over 24 hours.
Pressure tank
A larger pressure tank can reduce cycling frequency but does not eliminate energy demand.
How to size it
- Identify voltage and running power.
- Estimate daily equivalent run hours.
- Calculate daily Wh and apply losses.
- Verify 120/240V and surge compatibility.
A 1,000W pump running a cumulative two hours per day uses about 2kWh before losses, but its inverter requirement may be several times running power during startup.
Worked example
A 1,000W pump running a total of 90 minutes per day uses about 1.5kWh. At 85% usable energy, roughly 1.8kWh nominal is the energy minimum before reserve—provided the inverter can start the pump and supply the correct voltage.
Common buying mistakes
- Sizing only by daily kWh.
- Ignoring 240V requirements.
- Assuming generic pump startup values.
Well-pump backup is simultaneously an energy, voltage and motor-start problem; all three must pass.
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 →.