Whole-Home Battery Backup

An installed home battery is a different product from a portable power station: permanently wired, automatically transferring, and integrated with the panel.

How is whole-home backup different from a power station?

The decisive differences: an installed battery reaches hardwired loads — furnace, well pump, sump pump — and transfers automatically, without anyone present.

What is islanding on a home battery?

If you have or plan solar, this is the single most important thing to verify.

Many grid-tied solar systems shut down completely during an outage. It's a safety requirement — the inverter must not backfeed the grid while crews work on it.

Without islanding capability, your panels produce nothing precisely when you need them, and a battery has no way to recharge.

Homeowners discover this during their first outage with some regularity. If you have solar and expect it to help, ask specifically whether the system can island, and whether the battery is configured to charge from it during an outage.

With islanding solar plus a battery, a multi-day outage becomes genuinely manageable — the battery carries the night and solar refills it each day. Without it, the battery is a fixed reserve.

See charging a power station with solar for the same principle at portable scale.

Does a home battery back up the whole house?

Most installations back up a critical loads subpanel rather than everything.

Typically included:

• Refrigeration
• Some lighting
• Networking and device charging
• Furnace or boiler controls and blower
• Sump pump
• Well pump, if capacity allows
• Medical equipment circuits

Typically excluded:

• Air conditioning
• Electric water heating
• Electric range and dryer
• Electric resistance heat

The reason is capacity: those loads drain a battery in hours and require large inverter output. Some systems support them with load management, at a cost.

This mirrors the generator decision — see whole-house vs essential-circuits backup.

Two limits, not one

Energy capacity (kWh) — how much is stored. Determines duration.

Inverter output (kW) — how much power it can deliver at once. Determines what can run, and whether motor surges can be started.

A battery with plenty of stored energy but modest inverter output won't start a well pump. Both specifications matter, and they're sized independently.

Size yours with the home battery sizing calculator.

How long does a home battery last in an outage?

Essential loads — refrigeration, lighting, networking, a furnace blower cycling — add up to a manageable draw, and a typical home battery covers them for a matter of hours to a day.

What shortens it dramatically:

• Air conditioning or electric heat
• Well pump cycling frequently
• Cold weather, which reduces usable capacity
• Starting at partial charge, which is common if you haven't been watching

The honest summary: a home battery covers the common outage — hours, unattended, invisibly — very well. It does not cover four days in an ice storm unless solar is refilling it.

Value beyond outages

Unlike a generator, a battery earns its keep the rest of the year:

Time-of-use arbitrage. Charge when rates are low, discharge when they're high. Whether this is worth much depends entirely on your utility's rate structure.

Solar self-consumption. Store daytime production for evening use instead of exporting it — increasingly valuable where export compensation has fallen.

Demand charge reduction, where applicable.

Utility programs. Some utilities pay for access to home batteries during grid stress. Terms vary and are worth reading carefully.

These are why the economics can work even where outages are rare — see the home battery cost calculator and solar panel payback calculator.

What does whole-home battery installation involve?

Permitted, inspected work involving:

• A critical loads subpanel, usually
• An automatic transfer mechanism
• Inverter and battery placement, with clearances and often temperature requirements
• Utility interconnection approval, where solar or export is involved
• Permits — electrical, sometimes building, sometimes fire

Placement matters: batteries have temperature ranges, and some jurisdictions restrict indoor installation locations or require specific separations. Ask early.

Battery and generator

Not mutually exclusive, and the combination is coherent:

• The battery covers instant transfer and the quiet, unattended first hours
• The generator covers extended duration and can recharge the battery

For areas with long outages, this handles both failure modes — nobody runs outside for a two-hour outage, and a four-day outage is still survivable. See battery backup vs generator.

The portable end of whole-home

Below the installed-system tier, one portable unit genuinely crosses into circuit-backup territory — 240 V split-phase output that can feed a transfer switch:

The rest of the field, including the smaller classes, is in the power station picks.

Where to go next

• Battery backup vs generator
• LiFePO4 vs NMC batteries
• Do you need a home battery?

More in our generator and backup power guides.