How long will a Tesla Powerwall 3 last in a power cut?
A full Tesla Powerwall 3 (13.5 kWh usable) runs the fridge-freezer, heating controls, broadband, lights and phones for about 4 days 12 h in a British home, and about 2 days 7 h in an American home with a gas furnace. Running the whole house as normal, it lasts about 40 h 14 min.
Starting at a 20% reserve, the same essentials get about 21 h 39 min. A Powerwall 3 installed without the Backup Gateway 2 has no backup at all: it stops with the grid. With the gateway it islands the whole house in a fraction of a second.
The specifications that matter in a power cut
- Usable energy
- 13.5 kWh per unit
- Continuous output
- 11.04 kW
- Peak output
- Tesla gives a motor-start rating (185 A locked rotor) rather than a peak in kilowatts.
- Backup
- Whole house, with the gateway (Backup Gateway 2)
- Solar during a cut
- Yes
- Units per system
- Up to 4
- Chemistry
- LFP (lithium iron phosphate)
- Warranty
- 10 years, if it stays connected to the internet
- Sold in
- the UK and the US
Source: maker's datasheet, read 2026-09-26.
One, two or three of them
| What it runs | One | Two | Three |
|---|---|---|---|
| Fridge, internet, lights and phones | 5 days 12 h | 11 days | 16 days 13 h |
| The essentials, with the heating | 4 days 12 h | 9 days | 13 days 13 h |
| Essentials, heating, cooking and TV | 2 days 22 h | 5 days 20 h | 8 days 17 h |
| The whole house, as normal | 40 h 14 min | 3 days 8 h | 5 days 1 h |
| What it runs | Full | Half full | At a 20% reserve |
|---|---|---|---|
| Fridge, internet, lights and phones | 5 days 12 h | 2 days 18 h | 26 h 26 min |
| The essentials, with the heating | 4 days 12 h | 2 days 6 h | 21 h 39 min |
| Essentials, heating, cooking and TV | 2 days 22 h | 34 h 53 min | 13 h 58 min |
| The whole house, as normal | 40 h 14 min | 20 h 7 min | 8 h 3 min |
What it can run at once
Energy decides how long; output decides what. One Tesla Powerwall 3 supplies 11.04 kW continuously, so the essentials are easy but a big heater, a kettle or a car charger on top can be too much.
| Add this to the essentials | Everything at once | One Powerwall 3 |
|---|---|---|
| Electric kettle | 3.3 kW | Yes |
| Microwave, 1,000 W output | 1.8 kW | Yes |
| Portable induction hob | 2.1 kW | Yes |
| Space heater, 2,000 W | 2.3 kW | Yes |
| Electric car (3-pin "granny" charger) | 2.6 kW | Yes |
| Add this to the essentials | Everything at once | One Powerwall 3 |
|---|---|---|
| Microwave, 1,000 W output | 2.3 kW | Yes |
| Space heater, 1,500 W | 2.3 kW | Yes |
| Window air conditioner, 12,000 BTU | 1.9 kW | Yes |
| Sump pump | 1.6 kW | Yes |
| Well pump (1/2 hp) | 1.8 kW | Yes |
| Electric car (3-pin "granny" charger) | 2.2 kW | Yes |
Solar in a power cut
Solar panels wired to the Powerwall 3 keep charging it during a cut.
With 4 kWp of panels (London, 51.5°N), an average day's sun covers the essentials in every month except December. These are averages. A week of thick cloud, common in a British winter, can cut the panels to a fraction of this, so in the darker months plan on the battery alone and count the sun as a bonus.
| Month | Starting full |
|---|---|
| Jan | Keeps going |
| Feb | Keeps going |
| Mar | Keeps going |
| Apr | Keeps going |
| May | Keeps going |
| Jun | Keeps going |
| Jul | Keeps going |
| Aug | Keeps going |
| Sep | Keeps going |
| Oct | Keeps going |
| Nov | Keeps going |
| Dec | 22 days 18 h |
Do solar panels work in a power cut? explains why most systems stop, and what keeps them going.
How full is it when the power goes?
A home battery spends most days charging and discharging to save money, so a power cut finds it at whatever level it happens to be. In the evening in winter that can be close to empty. Most systems let you set a backup reserve that the battery will not use on ordinary days (Tesla calls it Backup Reserve; GivEnergy's app has a similar minimum charge for its emergency supply). The tables here show a full battery, a half-full one, and one sitting at a 20% reserve.
If a storm is forecast, charge it to full. Tesla's Storm Watch does this automatically when a weather warning is issued for your area; on other systems you raise the reserve or force a charge in the app.
No home battery? A power station for the essentials
A portable power station does the same job for the things that plug in, without an installer. The biggest ones hold a third to a half of a home battery. Here is how long each runs the fridge-freezer, the heating, the broadband, the lights and the phones, starting full:
| Power station | Capacity | UK home | US home |
|---|---|---|---|
| Zendure SuperBase V6400 | 6,438 Wh | 40 h 34 min | 19 h 50 min |
| EcoFlow DELTA Pro Ultra | 6,144 Wh | 39 h 47 min | 19 h 43 min |
| Jackery Explorer 5000 Plus | 5,040 Wh | 34 h 48 min | 16 h 41 min |
| Zendure SuperBase V4600 | 4,608 Wh | 31 h 13 min | 15 h 7 min |
| EcoFlow DELTA Pro 3 | 4,096 Wh | 27 h 45 min | 13 h 26 min |
The boiler or furnace is the catch: it is usually wired in, not plugged in, so a power station can only run it through a socket or a changeover switch an electrician fits. The boiler guide and the furnace guide explain how. Each station page has the full numbers and where to buy it.
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These are estimates from the site's model, not a maker's claim: stored energy × 94% through the inverter ÷ (what the house draws on average + about 30 W for the battery system itself). The sum is explained here.
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