PLAN THE POWER THAT MATTERS
What stays on
when the grid goes off?
Choose your essentials and compare Tesla Powerwall 3 and Fox ESS using US factory battery and inverter specifications.
Choose your essentials.
Appliance values below are examples. Confirm the running power and motor-start requirements on your actual equipment.
Factory specifications
US equipment specifications checked September 7, 2026. Choose the exact equipment in your proposal.
Tesla Powerwall 3 · US datasheetFox ESS ECS4000 · battery datasheetFox ESS H1 / AC1 US · inverter datasheetFACTORY BATTERY SPECIFICATIONS
1 Powerwall 3 + 0 Expansion
- Factory AC energy
- 13.50 kWh
- Continuous backup output
- 11.50 kW
- Factory motor-start rating, per inverter
- 185 A LRA · 1 second
Each Expansion adds 13.5 kWh, without adding inverter power. Up to three Expansions total connect to the leader Powerwall. The PV-only 15.4 kW mode is excluded from this battery-only estimate.
Usable energy available at start is the share of factory usable energy available for this scenario, not the battery app’s state-of-charge reading. Planning allowances are your assumptions. Tesla’s app Backup Reserve is saved for an outage; it is not subtracted here. Tesla’s energy rating is already AC; an extra fixed efficiency loss is not applied.
Energy-only estimate at the selected average use, with no solar recharging.
- Average demand
- 0.15 kW
- All selected loads running
- 0.27 kW
- Illustrative startup + other loads
- 0.98 kW
- Energy available in this scenario
- 13.50 kWh
Motor-start review needed. The appliance watt examples do not establish a match to the factory LRA rating. Confirm motor nameplates, surge duration and load management.
How the estimate works
Factory usable energy × available-usable-energy fraction × remaining fraction after your extra allowance × DC-to-AC allowance (Fox only) ÷ average load in kW. Fox usable DC energy is calculated from nominal energy × factory 90% depth of discharge. Tesla uses its factory AC energy rating without an additional conversion deduction.
Factory ratings are measured under specified conditions. Real runtime changes with load, temperature, age, state of charge, standby consumption and installed settings. Round-trip efficiency includes charging losses and is not used as discharge efficiency. Duty cycles and startup wattage are illustrative. No solar generation or simultaneous motor starts are modeled.
How Tesla Backup Reserve worksWhat changes with a generator?
A generator depends on fuel, equipment ratings and transfer controls. Review the running and motor-start requirements with your installer.
Discuss this backup plan →