Home battery vs standby generator: the same outage, two very different machines

Both machines answer the same question, what runs when the grid drops, and they are wrong for each other’s jobs. A battery is silent, instant and finite. A generator is loud, slower to start and, on a gas line, effectively unlimited. This page puts the two on the same scale, using the makers’ own figures, so the choice is about your outages rather than a brochure.

The two machines, from their spec sheets

Figure	Generac Guardian 22 kW (7043)	Tesla Powerwall 3	FranklinWH aPower 2
Continuous output	22 kW on propane, 19.5 kW on natural gas	up to 11.5 kW	10 kW
Motor start	Rated to start whole-house loads	185 A locked rotor	185 A locked rotor, 15 kW for 10 seconds
Energy on hand	As long as fuel flows; Generac lists 216 cubic feet of natural gas an hour at half load	13.5 kWh per unit	15 kWh per unit
Noise	About 67 dB(A)	Silent	Silent
Switchover	Seconds, automatic	Milliseconds, automatic	Milliseconds, automatic
Exhaust	Carbon monoxide; outdoors only, away from openings	None	None
Safety listing stated	Generator standards	UL 9540	UL 9540, UL 1973

Figures from Generac’s Guardian spec sheet and dealer listings that reproduce it, Tesla’s Powerwall 3 datasheet and FranklinWH’s aPower 2 datasheet, read September 10, 2026.

Runtime: finite against indefinite

A generator on a natural gas line runs until the utility stops supplying gas, which in most outages is never. On propane it runs until the tank is empty, and Generac’s half-load figure of 216 cubic feet of gas an hour is the scale of the appetite: a big machine burning fuel all night to keep a refrigerator cold.

A battery runs for its capacity divided by the load, and the load is the decision. At the 2.5 kWh a day of essentials the home battery backup page adds up, a single 13.5 kWh Powerwall 3 is about five days. At the 28 kWh a day the average American household uses per EIA, it is about eleven hours. Same battery, a factor of ten apart, which is why every battery conversation starts with what stays on. Solar changes the battery’s answer, because a sunny day refills it; nothing changes the generator’s.

Start-up: where portable batteries lose and installed ones do not

The load that separates the classes is a motor. Franklin’s 1/2 HP well pump motor draws about 32 A locked rotor at 230 V, and a central air conditioner’s compressor is larger still. A standby generator is sized for those starts by design. So are the installed batteries: Tesla and FranklinWH both quote a 185 A start capability. Portable units mostly are not, and the well pump page shows how few clear the bar. If your list has a 240 V motor on it, you are choosing between a standby generator and an installed battery, not a portable one.

The trade-offs that are not on the spec sheet

Maintenance. A generator is an engine: oil, filters, a weekly self-test, a battery of its own to start it, and a service visit. A home battery has no moving parts and a 10 to 15 year warranty; FranklinWH’s is 15 years.

Fuel risk. Propane deliveries stop in the storms that cause outages, and a natural gas line can be interrupted in an earthquake or a hard freeze; the February 2021 Texas event took gas supply down with the grid. A battery’s risk is the opposite: a long outage with no sun.

Placement. A generator needs a pad outdoors, clearance from windows and doors, and a gas line run. A battery needs a wall, indoors or out, and a gateway at the panel. Both need an electrician and a permit; the transfer switch page explains what that work is.

Carbon monoxide. The red callout at the top of this page is the only thing on it that is not a trade-off. A generator produces CO, and the deaths cluster in exactly the storms it was bought for. A battery does not.

When each is right

• Battery: outages of hours to a couple of days, a household that wants silence and instant switchover, a home with or planning solar, anywhere fuel delivery is unreliable.
• Generator: a week-long outage with no sun, a house that must run everything including central air, a natural gas line already at the house.
• Both: the long-outage household that wants the battery’s manners day to day. The battery carries the house; the generator runs a few hours to recharge it at full load, its most efficient point, and is off the rest of the time. Several battery makers sell a generator input for exactly this.

What this does not cover

Portable gas generators, the wheeled kind, are a different product with the same exhaust and none of the automatic switchover; we do not rank them. The portable battery side of the comparison, the units you plug an appliance into, is the refrigerator and sump pump pages, where the runtime tables live.