What can a home battery back up?
A suitably designed home battery system can supply selected household circuits during an outage. Broader backup may be possible, but the equipment, electrical design and loads must be assessed together. A battery does not automatically mean every appliance can run at once.
Start with priorities rather than a promise of “whole-home” operation. Your design should identify supported loads and any equipment that needs to stay off during backup.
Choose the loads that matter to you.
Make a list of essential lighting, refrigeration, internet equipment and other priorities. Add larger equipment separately: heating, cooling, pumps, cooking and vehicle charging can change the design substantially.
Give the specialist equipment model details where available. A device’s running demand and the brief demand when its motor starts can be different. Do not assume a familiar appliance is suitable simply because its average consumption looks modest.
kW and kWh answer different questions.
- Power, in kilowatts (kW)
- How quickly a system can deliver electricity. It helps determine which loads can run together.
- Energy, in kilowatt-hours (kWh)
- How much electricity is stored or used over time. It helps determine how long supported loads may run.
More stored energy does not necessarily mean more instantaneous output. The inverter, battery configuration and backup controls all matter. Compare a proposal’s usable energy and backup output, not just one headline number.
Why there is no single runtime for a home.
The same battery can last longer under lighter demand and less time under heavier demand. A useful assessment considers:
- The battery’s charge when the outage begins.
- Usable capacity and any operating reserve.
- Which loads run, for how long, and whether they cycle on and off.
- Conversion losses and system standby consumption.
- Temperature, battery condition and operating limits.
- Whether a compatible, approved recharging source is available during the outage.
Ask for scenarios based on your actual loads and stated assumptions. A runtime illustration is not a guaranteed duration.
HYPOTHETICAL EXAMPLE
How average demand changes runtime.
Assume 8 kWh is available to household AC loads after allowing for the starting charge, operating reserve, conversion losses and standby consumption. This is a chosen example, not a PowerQ specification or a recommended system size. Assume no recharging during the outage.
Illustrative runtime = available energy (kWh) ÷ average household demand (kW).
| Average load | Calculation | Runtime |
|---|---|---|
| 0.5 kW | 8 ÷ 0.5 | 16 hours |
| 1 kW | 8 ÷ 1 | 8 hours |
| 2 kW | 8 ÷ 2 | 4 hours |
These are arithmetic scenarios, not appliance ratings or guaranteed durations. Real loads cycle, and temperature, battery condition and operating settings can change available energy. Use measured loads and the proposed configuration for a household assessment.
Energy is only one test.
The inverter must also support the simultaneous running demand and brief motor-starting demand. A pump can exceed a system’s starting capability even when plenty of energy remains. The table does not establish which appliances the system can power.
Comparing options? Read the battery versus standby generator guide.
Make the operating plan part of the conversation.
Ask which circuits are supported, what happens when the grid fails and returns, and how you will know the battery’s state of charge. Confirm any manual steps and what happens if stored energy runs low.
Keeping more energy in reserve for outages can reduce the energy available for daily rate shifting. Decide which goal matters most, then have the specialist confirm settings appropriate to the system.
Continue with the system overview or the consultation checklist.