The difference that decides it
Everything else in this comparison follows from one fact.
A battery stores a fixed amount of energy. When it is empty, it is empty, and the only things that refill it are the grid — which is out — or solar, which depends on weather and daylight.
A generator makes energy from fuel. Its capacity is however much fuel you can get, which during a short outage is unlimited and during a regional multi-day event is its own problem.
So the question is not which is better. It is how long your power goes out for, and the honest answer for most households is that they do not know — which is what the outage duration page exists to fix.
Side by side
| Installed home battery | Standby generator |
|---|
| Duration | Fixed — hours, unless solar refills it | Unlimited while fuel arrives |
|---|
| Noise | Silent | Loud, and it runs all night |
|---|
| Changeover | Instant — the lights do not flicker | 10-30 seconds while it starts |
|---|
| Maintenance | Essentially none | Annual service, fuel management, exercise runs |
|---|
| Fuel | None | Natural gas line, or propane deliveries |
|---|
| Everyday value | Time-of-use arbitrage, solar self-consumption | None — it sits idle |
|---|
| Lifespan | Warranty typically 10 years | Decades with servicing |
|---|
| Cold weather | Reduced capacity, usually managed by heating | Starts harder; propane vaporizes less readily |
|---|
Characteristics are general to the product classes. This site does not publish installed-system prices; those depend on your panel, your site and your installer, and any figure we quoted would be wrong for most readers.
The energy arithmetic, plainly
A single home battery unit typically stores somewhere in the low tens of kilowatt-hours. Run against a modest critical-load list, that is a useful number of hours; run against a whole house including air conditioning, it is not.
| Load | Average draw | Hours from 13.5 kWh |
|---|
| Critical loads only | 300 W | About 45 hours |
|---|
| Critical loads plus a furnace blower | 600 W average | About 22 hours |
|---|
| Normal household use, no heating or cooling | 1,200 W | About 11 hours |
|---|
| Household with central air running | 3,500 W average | Under 4 hours |
|---|
13.5 kWh is used as an illustrative single-unit capacity. Hours are capacity divided by average draw; real systems reserve some capacity and lose a little to conversion.
Note the shape. Managed carefully, a home battery covers a two-day outage comfortably. Used as though the grid were still there, it covers an evening. That difference is behavioral rather than technical, and it is where most disappointment comes from.
Solar changes the answer completely
This is the single biggest factor and it is often left out of the comparison.
A battery without solar is a fixed store — you get one tankful. A battery with a decent array refills every sunny day, which turns a two-day capability into an indefinite one, silently, with no fuel.
That is the configuration where a battery genuinely beats a generator, and it is why most installed home batteries are sold alongside panels rather than on their own.
The caveat is seasonal. Winter production in most of the United States is a fraction of summer, and winter is when the long outages happen — the solar sizing page covers what an array actually returns.
The two things only a battery does
1. It pays for itself between outages. Time-of-use arbitrage — charging when power is cheap and discharging when it is expensive — and storing your own solar production instead of exporting it. A generator earns nothing for the 8,750 hours a year it is idle.
2. The changeover is invisible. A battery switches in milliseconds, so clocks do not reset and computers do not reboot. A standby generator takes ten to thirty seconds to start and transfer, which is a brief outage every time.
The two things only a generator does
1. It runs for a week. The scenario that actually justifies whole-house backup — a regional ice storm or a hurricane aftermath — is exactly the one a fixed store of energy handles worst.
2. It carries large loads continuously. Central air conditioning, electric heat, a well pump and an electric range are loads a generator sized for them will run indefinitely and a battery will run briefly.
The configuration that is often best
Both, and it is less extravagant than it sounds because the two are sized against different problems.
A modest battery handles the common case — the several short outages a year — silently and automatically, with no fuel and no noise. A portable generator handles the rare multi-day event, gets pulled out twice a decade, and costs a fraction of upsizing the battery to cover a week.
The technology comparison covers the underlying trade in more detail, and the home battery systems page covers the units that sit between a power station and an installed system.
The short version
- Hours-long outages: battery. Silent, instant, no maintenance.
- Days-long outages: generator. Fuel has no capacity limit.
- Solar changes the answer more than any other single factor.
- A battery earns money between outages. A generator does not.
