How much battery backup do you need?
Walk through your home, tick what must keep running and set the hours — get the battery size, the start-up peak and setups you can check against any model.
EIA-861 Reliability, major event days included. /outages/
1 Approximate values: estimated from motor or heater power and typical figures published online, not from a manufacturer chart. Check your appliance label.
Your numbers
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Inverter efficiency 88%, usable depth of discharge 90%, reserve 20%. Full method: How we calculate →
How the calculator works
- Pick what must run and for how many hours a day. Motors such as fridges and pumps switch on and off, so the calculator counts only the time they run.
- Set the outage length or pick your state to use its typical outage from EIA data.
- Read four numbers: battery size (Wh), start-up peak (W), solar to refill it and generator size. Then check any model against them.
Example: essentials for 24 hours
Refrigerator (with freezer), Wi-Fi router + modem/ONU, LED lighting (5 bulbs), CPAP (no humidifier), Sump pump 1/2 HP use about 2,696 Wh in 24 hours. With losses and a reserve that is a 4,085 Wh battery that can start 2,357 W, or a generator of at least 2,947 W. Step by step on how we calculate; ready-made lists in scenarios.
Common questions
How big a battery do I need to run a refrigerator for 24 hours?
About 1,528 Wh for a typical 120 W refrigerator that runs 35 % of the time, after inverter losses, usable depth of discharge and a 20 % reserve. The station must also start it: about 600 W for a moment.
What size generator do I need for a refrigerator and a sump pump?
At least 2,838 W running: the two together peak at about 2,270 W when the pump starts while the fridge runs, plus 25 % headroom.
How long will a 1,000 Wh power station run a CPAP?
About 18.9 hours for a 35 W CPAP without the humidifier, or 2 nights of 8 hours. The heated humidifier can triple the draw.
Can a power station run a whole house?
Essentials, yes: a fridge, internet, lights, a CPAP and a sump pump need about 4,085 Wh of battery for 24 hours. Central air, electric heat and water heaters do not fit: one 1,000 W air conditioner alone uses about 12,000 Wh a day. That is home-battery or standby-generator territory.