Home battery backup power, explained.
Last updated 2 October 2026
Whole home versus essential circuits
Some battery installs back up your entire switchboard, so every circuit in the house keeps running during an outage. Others back up only a chosen subset, essential circuits, wired to a separate backup sub-board, usually things like fridges, lighting and some power points. Which one you get depends on the battery's own power rating, your home's total load, and how the installer wires it, not just which brand you choose.
Backup power rating
A battery system has a continuous power rating (in kW) and often a higher, short-duration peak rating for starting things like fridge compressors, air conditioners or pumps. That rating sets a ceiling on what can actually run at once during an outage, a battery with plenty of stored energy can still trip if too much is drawn from it at the same moment.
What happens in an outage
When the grid goes down, a backup-capable system disconnects from the grid and switches to powering your home (or your essential circuits) from the battery, usually automatically and within a short gap. Solar panels can keep charging the battery during the day if the system is configured for it, extending how long backup lasts.
Why islanding support matters
For safety, grid-connected inverters are required to shut off during a blackout, so they don't feed power back into lines that might have people working on them. "Islanding" is the capability that lets a system safely separate your home's circuit from the grid and keep running on battery power alone. Without it, your battery can't provide backup at all during an outage, no matter how much energy it holds.
What our data actually says
Most manufacturers don't publish a specific whole home versus essential circuits claim, that's usually a design decision your installer makes for your specific home. Two things are explicitly stated in the model data we track:
- Tesla Powerwall 3 is positioned by Tesla for homes wanting whole home backup, with a continuous rating of 11.04 kW continuous AC; 185A LRA motor-start capability.
- Enphase IQ Battery 5P discharges to 100% depth of discharge in backup, versus 90% in normal grid-connected use, so more of its stated capacity is available when it matters.
For every other model, confirm whole home versus essential circuits capability, and the specific power rating that applies to your home, directly with your installer.
See also how warranty terms work and how long batteries last.
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See every battery brand and model →Common questions
Will my solar panels work during a blackout without a battery?+
Generally no. Standard grid-connected solar inverters shut off during an outage for safety, whether or not you have panels. Backup power specifically requires islanding support, which is a battery system capability, not something solar panels alone provide.
Can I choose which circuits are backed up?+
If you're going with essential circuits rather than whole home backup, yes, your installer wires a chosen subset to a backup sub-board. Decide this during installation, since it affects the electrical work involved.