Understanding sump pump backup sizing
Why sump pumps are one of the cheapest loads to back up
An 800 watt sump pump sounds like a meaningful draw, but it only runs in short bursts, often 20 to 30 seconds at a time, several times an hour during heavy rain. Total cumulative runtime across an entire storm rarely exceeds 20 to 30 minutes, which keeps the energy need, and the battery capacity required, very small. This is why dedicated sump pump backup batteries are usually compact units well under 1 kWh, far smaller than what a refrigerator or medical device would need, and correspondingly far cheaper, as the quick financing comparison tool in our Financing category would confirm against a full whole-home system.
Why sump pumps and power outages happen together
The same severe weather that causes flooding, heavy rain and high wind, is also the most common cause of grid power outages. This means the moments a sump pump matters most are exactly the moments it's most likely to lose power, which is why sump pump backup is considered high priority despite its tiny energy footprint, a risk pattern documented in FEMA's flood preparedness guidance. The storm season planning tool covers this overlap for backup planning more broadly.
Dedicated battery versus whole home battery system
Many hardware stores sell dedicated sump pump backup batteries, compact sealed units installed directly next to the pump that switch on automatically when grid power fails. These are a low-cost, purpose-built option precisely because the energy requirement is so small, a category ENERGY STAR's product database lists separately from larger whole-home battery systems. If you already have a whole home battery system for other backup needs, it will easily also cover the sump pump without needing a separate dedicated unit. The critical loads calculator lets you add a sump pump into a broader critical loads list.
What to do with this number next
If you're planning backup for a whole storm season rather than a single event, the winter storm planning tool takes a broader view. For a complete critical loads picture including the sump pump, refrigerator, and other essentials together, the well pump backup tool combines them into one battery size. The inverter surge rating this pump's motor requires is covered in the inverter sizing for motor loads calculator in our Inverters & Equipment category.