Generator vs battery backup for a home outage
A generator makes power as long as you feed it fuel; a battery stores a fixed amount of energy and needs a recharge. For short outages and indoor, quiet use a battery fits; for multi-day outages or heavy loads a generator covers more per refill.
Numbers updated from the published specs.
The core difference
A battery holds energy in watt-hours (Wh). When it is empty, it is empty until the grid returns or solar refills it. A generator holds no energy itself. It turns fuel into power, so run time is the size of the fuel supply divided by the burn rate.
The published catalogue on this site lists 193 power stations with a median capacity of 1,024 Wh and a median output of 1,800 W. It lists 31 home batteries, median 10,000 Wh and 7,200 W. For 390 portable and inverter generators the median rated output is 4,000 W. The 35 standby generators have a median rating of 22,000 W.
A worked example: one day of essentials
Take a refrigerator, router, LED lights, phone charging and a CPAP at the default hours in our appliance data. That is 1,806 Wh per day, with 222 W if everything runs at once.
| Battery | Generator | |
|---|---|---|
| Size needed for 24 h | 2,737 Wh | about 222 W output |
| Per 24 h | one full charge | about 2.2 L (0.6 gal) of fuel |
| Median published unit | 1,024 Wh | 4,000 W |
Battery size = daily Wh ÷ (0.88 inverter efficiency × 0.9 usable depth) × 1.2 reserve. Fuel uses the calculator rule of 0.4 L per kWh at about half load; a real engine varies.
Run time and fuel
A battery's run time is fixed by its capacity. At the calculator's constants, a refrigerator (with freezer) averaging 42 W lasts about 15.7 hours per 1,000 Wh, so a median station runs it about 16 hours.
For a generator, the same rule gives 0.4 L per hour at 1,000 W and 1.6 L per hour at the median rated 4,000 W. One US gallon is 3.785 L, so that is about 0.42 gal per hour. Among generators that list a tank size, the median tank is 15.2 L (4 gal), 348 models in all.
Recharging: a battery refills from the grid when power returns, from a car outlet or from solar panels. Solar adds energy only in daylight. A generator is refilled in minutes.
Noise, exhaust and indoor safety
An engine is loud. Among 178 generators that list noise, the median is 64 dB. Makers measure at different distances and loads, so read the spec page before comparing.
Engines also make carbon monoxide (CO), a gas you cannot see or smell. Never run a generator indoors, in a garage or near an open window. 230 of the 390 published generators list a CO shutoff feature; it is a backup, not a reason to move one indoors. A battery has no exhaust.
Surge and what each covers well
Motors, such as a refrigerator compressor, draw a spike when they start. Our data lists the refrigerator (with freezer) at 120 W running and 600 W at start. Spec sheets list a surge figure; check it against your largest motor. See the well pump guide for a hard case.
Batteries cover well: short outages, small essential loads, quiet or indoor use, apartments, and homes with solar. Generators cover well: multi-day outages, large 240 V loads, and long cold or hot spells where a battery would drain. Standby generators start on their own; see standby generators.
Maintenance
A generator needs oil changes, fresh fuel, a spark plug and a test run at intervals set in its manual. A battery needs little: keep it charged and within its temperature range. Error codes for both are listed under error codes.
Choose by outage length
Check how long outages last where you live on the outages by state pages. Then enter your own appliances in the calculator. Browse power stations, home batteries and inverter generators. Connecting either to the house wiring is covered in transfer switch vs interlock.
FAQ
Can I run a portable generator in the garage?
No. Generators make carbon monoxide, which is colorless and odorless. Run one outdoors, well away from doors, windows and vents, even if the garage door is open. A power station or home battery has no exhaust and can sit indoors.
How long will a power station run a refrigerator?
With the calculator constants (0.88 inverter efficiency, 0.9 usable depth, 1.2 reserve), a fridge averaging 42 W runs about 15.7 hours per 1,000 Wh. A 1,024 Wh station, the median published here, gives about 16 hours.
Which is quieter?
A battery. It has no engine; only a fan runs under load. Generators are rated in decibels, and the published median is 64 dB for the models that list a figure. Test conditions differ between brands, so compare like with like.
Do I need a transfer switch?
To power hardwired circuits from a generator or home battery, yes. Plugging into a wall outlet to backfeed the house is dangerous. See the transfer switch guide for the options.
Figures come from the published product data on this site and the constants in the calculator. Check each manufacturer's spec page.