Sump backup
Size sump pump backup from the pump and the outage.
Horsepower alone is not enough. Use the measured running draw, starting requirement, pump cycle, and protected hours.
Direct answer
A 1/3 hp sump pump drawing about 800 W at a 15% storm duty cycle may run 6 to 9 hours on one 100 Ah AGM battery. Starting current and measured draw must still be checked.
Before the hardware
Collect these four inputs.
- 01Pump nameplate
- 02Measured running draw
- 03Duty cycle
- 04Protected hours
Decision table
Reference runtime table
| Pump case | Battery | Storm duty | Protected time |
|---|---|---|---|
| 1/3 hp, about 800 W running | 1 × 12 V 100 Ah AGM | 15% | About 6 to 9 h |
| 1/3 hp, about 800 W running | 2 × matched 12 V 100 Ah AGM | 15% | About 12 to 18 h |
This is a screening range, not a warranty. Pump start, inverter loss, battery age, temperature, and real cycling change runtime.
What makes it work
Three choices that need to be checked together.
Deep-cycle battery
Choose capacity from measured pump watts, storm duty, and protected hours.
View the categoryInverter and charger
Continuous and starting power must both exceed the pump requirement.
View the categoryBattery maintainer
A compatible maintainer can support storage, but it does not replace a backup controller.
View the categoryA sump backup protects a motor load. Network gear and control panels use a different standby duty, so review standby UPS batteries when the protected load is electronics rather than the pump itself.
Help around the hardware
A product record does not replace a system review.
Free sizing review
A load worksheet review with the assumptions, missing inputs, and a hardware direction.
See all servicesCustom battery bank assembly
Series or parallel configuration with cables cut, crimped, and labelled after compatibility review.
See all servicesKeep checking
The method and terms used here.
Read the sizing method
See the assumptions, suppression rules, and evidence standard used here.
Read the guideCheck the energy glossary
Confirm the meaning of capacity, energy, current, and autonomy.
Read the guideHonest limits
Know before you buy
- A dedicated backup sump pump system is not yet in the catalog.
- Horsepower is not enough. Measure running draw and confirm starting current.
- Battery age, cold temperature, inverter loss, and real storm cycling reduce runtime.
Common questions
Short answers, limits included.
Can I size backup from pump horsepower alone?
No. The nameplate, measured running watts, starting current, and storm duty are all required.
Does a second battery double runtime?
Two matched batteries at the same voltage can roughly double stored energy. Wiring, age, and protection still need review.
Can a maintainer power the pump?
No. A maintainer keeps a compatible battery charged. It is not an inverter or backup transfer controller.
Is the 6 to 9 hour range guaranteed?
No. It is a screening range for one reference case. The real pump and battery must be tested.