Whole-home battery backup or essentials only?

Two ways to wire backup

With essentials-only backup (installers call it partial-home or critical loads), the electrician moves a handful of circuits to a separate subpanel: typically the fridge, some lights, a few outlets, the internet equipment, and sometimes the furnace blower or a well pump. In an outage, only those circuits stay on.

With whole-home backup, the battery takes over the main panel, so anything in the house can run. In practice, that doesn’t mean everything can run at the same time. The battery has a power limit, and the heavy appliances (air conditioning, electric heat, an electric range, a car charger) can exceed it on their own. Whole-home systems usually rely on load management, either in the battery’s own gateway or in a smart panel, to switch big loads off when needed.

What counts as essential

These are typical figures. Your appliances’ labels, or a plug-in energy meter, will give you better numbers.

Appliance	Typical running power	Typical energy per day
Fridge-freezer	100 to 200 W while the compressor runs	about 1 to 2 kWh
Router and modem	10 to 20 W	about 0.3 to 0.5 kWh
LED lighting	5 to 10 W a bulb	about 0.3 kWh for a few rooms
Gas furnace blower	300 to 800 W	about 1 to 3 kWh in winter
Sump or well pump	500 W and up, big start-up surge	depends on use
CPAP	30 to 60 W	about 0.3 to 0.5 kWh
Central air (3 ton)	about 3 to 4 kW, big start-up surge	20 kWh or more on a hot day
Electric water heater	about 4.5 kW	5 to 15 kWh
EV charger	7 kW and up	as much as you let it

Add up the essentials and most households land at about 3 to 7 kWh a day. The average American home uses roughly 28 kWh a day, according to the EIA, and the difference is almost all heating, cooling, hot water and cooking.

Power and energy, side by side

Two numbers decide which approach works.

Power (kW) is how much the battery can deliver at once. A Tesla Powerwall 3 is rated at 11.5 kW continuous. An Enphase IQ Battery 5P is 3.84 kW per unit, so they’re usually installed in groups. A FranklinWH aPower 2 is listed at 10 kW. Essentials rarely need more than 2 to 3 kW at once. Whole-home use can need 10 kW or more when the air conditioning and the well pump start together.

Energy (kWh) is how long the battery lasts. A 13.5 kWh battery covers essentials for two or three days without solar, but a whole house for perhaps half a day.

What each approach costs

• Essentials only: one battery of 10 to 15 kWh, plus a critical loads panel. EnergySage puts a typical Powerwall 3 at about $13,500 installed before incentives in 2026.
• Whole-home: often two or three batteries, or one battery with a smart panel to manage loads. Expect the bill to rise roughly in step with the number of batteries.
• Portable route: a 1 to 4 kWh power station and extension cords, from a few hundred to a few thousand dollars, with no installation. It won’t run hard-wired appliances such as a furnace or well pump without a transfer switch.

Which should you choose?

Essentials only makes sense if:

• your outages are usually hours, not days,
• you heat with gas, so the furnace only needs its blower,
• you can live without air conditioning for a day,
• budget matters more than convenience.

Whole-home makes sense if:

• your home is all-electric, especially with a heat pump or electric heat,
• outages in your area last days, or come with summer heat where AC is a health issue,
• you rely on a well pump,
• you’ll also use the battery daily for time-of-use savings or a utility program, which spreads the cost over more than outages.

There’s a middle path that many installers now suggest: one larger battery backing up the whole panel, with load management that sheds the big appliances automatically. You get the convenience of everything being available, and the battery decides what waits.

A sensible order to do it in

1. List what you can’t do without, and add up the daily kWh.
2. Check the starting needs of anything with a motor: fridge, pumps, AC.
3. Decide how many hours or days you want to cover. The EIA found the average US customer was without power for about 11 hours in 2024, but that average hides long storm outages in some regions.
4. Get quotes for both essentials-only and whole-home, priced per usable kWh, so you can see what the extra coverage costs.

For the costs behind those quotes, see what solar battery storage really costs, and for the basics of how backup works, start with home battery backup, explained.