Tool · Backup power
Battery size calculator
Tick what you want to keep running in a power cut and how long it should last. You'll see how big a battery you need, how much power it has to deliver, and which power stations fit.
With no recharging. Solar panels or the grid coming back shorten what you need.
The compressor runs about a third of the time.
Without a heated humidifier. Check your label.
Usually hardwired, so it needs a transfer switch or inlet.
Not sure of a figure? The label or power adapter gives the watts. For a fridge, divide the yearly kWh on its energy label by 365, then adjust the hours until the kWh a day matches.
You need about
2.3 kWh of battery
Pick something to keep running
Tick at least one appliance in the list.
A 1 kWh portable power station
The most common size. Add folding solar panels if you want it to last through a longer outage.
A 2 kWh power station
Or a 1 kWh unit with solar panels to top it up during the day.
A large or expandable power station
Units of about 3 to 5 kWh, or a 2 kWh unit with an extra battery. Many can feed home circuits through a transfer switch.
An expandable home power station or an installed battery
This is home battery territory: an expandable system, or a permanently installed battery of 10 to 15 kWh.
More than one home battery
That's more than a single home battery stores. Back up fewer things, or pair a battery with a generator for long outages.
No portable unit in our finder delivers that much power at once. Run the big loads one at a time, or look at installed home batteries.
Power stations in our finder that fit
- Jackery Explorer 1000 v2 On its own
- EcoFlow DELTA 3 Plus With extra batteries
- Anker SOLIX C1000 Gen 2 On its own
- BLUETTI AC180 On its own
- Jackery Explorer 2000 v2 On its own
- Jackery Explorer 2000 Plus With extra batteries
- EcoFlow DELTA Pro 3 On its own
None of the single units we list is big enough. See our home battery backup guide.
Compare runtimes in the finder- Inverter efficiency 85%
- Battery starts full
- No recharging
An estimate for planning. If someone relies on medical equipment, check the device's label and ask the supplier about backup.
How this calculator works
- 1. Energy per day
- 2. Whole backup
- 3. Battery size
- 4. Power output
A power station loses some energy turning battery power into mains power, so we divide by 0.85. For output, we add up everything you ticked as if it all runs at once, then add the single biggest start-up surge: motors in fridges, freezers and pumps draw several times their running power for a moment, but rarely all at the same instant.
Ways to need a smaller battery
- Keep the fridge shut. A full freezer stays safe for about 48 hours with the door closed, so it can often wait.
- Skip heat. Space heaters, kettles and hair dryers use more in an hour than a fridge in a day.
- Charge things early. Top up phones, laptops and power banks before a storm arrives.
- Add solar. Each 100 W of folding panels gives roughly 0.3 to 0.4 kWh on a sunny day. See solar generators for home backup.