Home battery vs generator for power outages

• Outages of a few hours, a few times a year: a battery covers them silently, with no fuel to store and nothing to start.
• Outages that last days (ice storms, hurricanes): a generator, or a battery paired with solar panels that can recharge it every sunny day.
• You need to run central air, a well pump or an electric range during the outage: a large standby generator, or a battery system sized for those loads, which gets expensive fast.
• You just want the fridge, lights, internet and phones: a portable generator or a portable power station is the cheapest option.

	Home battery	Standby generator	Portable generator	Portable power station
Typical size	13.5 kWh per unit	22 kW	5,500 W	about 1,000 Wh
Fuel	Stored electricity (recharged from the grid or solar)	Propane or natural gas	Gasoline (some propane or dual fuel)	Stored electricity
Starts	Automatically, in a blink	Automatically, within seconds	By hand, then cords or a transfer switch	Plug things into it
Runs for	Hours to a day, unless solar recharges it	Days, as long as the fuel lasts	About 11 hours per 6-gallon tank at half load	Hours for small loads
Noise	Near silent	Loud, outside the house	Loud, outside the house	Silent
Where it goes	Garage or wall, indoors or out	Concrete pad outside	Outside, away from doors and windows	Anywhere
Upkeep	Little	Weekly self-test run, yearly service	Oil changes, stale fuel, test runs	Recharge now and then

Generators of every kind make carbon monoxide. They must run outdoors, well away from doors, windows and vents, never in a garage, even with the door open.

A home battery gives back about 90% of its rated capacity as usable power after inverter losses, which is what our battery runtime calculator assumes. A 13.5 kWh unit delivers about 12 kWh. Kept to essentials, a fridge, lights, internet, a furnace fan and a few outlets, a home averages around 1.2 kW, so that's about 10 hours. Turn on a 3-ton central AC (about 3.5 kW more) and it drops to about 2.6 hours.

To cover two days of essentials at 10 kWh a day, you need about 22 kWh of battery, which rounds up to two 13.5 kWh units. Our battery size calculator does this sum for any load and number of days.

A standby generator runs as long as its fuel lasts. A 22 kW propane unit burns about 1.5 to 2.1 gallons an hour at half load, depending on the model's spec sheet. A 250-gallon tank is filled to 80% for safety, so it holds about 200 usable gallons: roughly 4 to 5½ days of continuous running. A natural gas unit draws from the utility line and runs as long as gas keeps flowing. The propane tank duration calculator works it out for your tank and generator.

A portable generator at 5,500 W burns about 0.55 gallons of gasoline an hour at half load, so a 6-gallon tank lasts about 11 hours. Around the clock, that's 13 gallons a day, all of which you need to store safely and buy before the storm. Check yours in the generator runtime calculator.

A portable power station of about 1,000 Wh keeps a refrigerator going for about 15 hours (60 W on average) or a CPAP machine for about 22 hours (40 W) after inverter losses. See the power station runtime calculator.

What a generator can start depends on its watts; what a battery can start depends on its inverter's power rating, which is a separate number from its kWh.

Motors are the catch. They pull two to three times their running watts for a moment when they start. In our generator calculators, a refrigerator runs at about 700 W but starts at about 2,200 W; a 1 HP well pump runs at 1,000 W and starts at 3,000 W; a 3-ton central AC runs at 3,500 W and starts at about 7,000 W.

• Portable generator (5,500 W): fridge, sump pump, lights, TV and internet at the same time, with room to spare. Adding a well pump or a window AC takes it to its limit, so start the big motors one at a time. Central AC doesn’t fit. See exactly what fits in what a 5,500 W generator can run.
• Standby generator (22 kW): most of a typical house, central AC included, with a properly sized transfer switch.
• One home battery unit: essentials easily; central AC or a well pump only if the unit's inverter can handle the starting surge. Check the continuous and peak kW on the spec sheet, not just the kWh. Heavy loads like an electric range, dryer or water heater drain a single unit in a few hours, so most battery owners back up a "critical loads" panel rather than the whole house.
• Power station: fridge, phones, laptop, lights, CPAP, a router. Not a sump pump or anything with a big motor, unless the station's surge rating says so.

Battery: about $1,000 per kWh installed is the default in our calculators, so $13,500 for one 13.5 kWh unit and $27,000 for two. After that there's no fuel cost; recharging from the grid costs only what the stored power costs, $2.45 for a full 13.5 kWh at the national rate.

Standby generator: about $9,000 installed for a 22 kW unit (our default, from a $5,000 to $15,000 range). Then three running costs, outage or not:

• the weekly self-test, which burns roughly 13 gallons of propane a year;
• the battery charger and block heater, which draw about 40 W around the clock, 350 kWh a year, about $63.56 at the national rate;
• maintenance of about $200 to $400 a year.

The standby generator cost calculator adds them up for your state.

Worked example. Compare one 13.5 kWh battery ($13,500) with a $9,000 standby generator burning 1.5 gallons an hour, with $300 a year of maintenance, and propane at $3.00 a gallon for round numbers:

• With 40 outage hours a year: 40 × 1.5 × $3.00 = $180 of propane a year. Over 10 years, $9,000 + $1,800 + $3,000 = $13,800, about the same as the battery.
• With 120 outage hours a year: $540 of propane a year, $17,400 over 10 years. The battery's purchase price doesn't change, but a single unit can't carry a house through a 3-day outage without solar.

That's the pattern: for short outages the costs are close and the battery is easier to live with; for long outages the generator is the one that keeps running. Run it with your own state's propane price in the battery vs generator calculator.

Portable generator: the cheapest to buy by far, but the most expensive power per kWh. At $3.00 a gallon, a 5,500 W unit at half load makes power for about 60 cents per kWh, against 18.2¢/kWh from the grid nationally. Fine for a day or two a year, painful for a week. The generator fuel cost calculator prices it with your state's fuel.

1. How long were your last few outages? Your utility's outage history or your own memory is the best input. If they're rarely over 8 hours, a battery or a portable setup covers them.
2. What has to stay on? Write down the must-haves with their watts. A well pump or a medical device changes the answer; a freezer full of food might too.
3. Do you have, or plan, solar? A battery with solar can recharge every day and ride through a long outage on essentials. Without solar, it's a one-time tank.
4. Is natural gas at the house? A natural gas standby generator needs no fuel deliveries; a propane one needs a tank and refills.
5. Who will run it? Standby units and batteries switch on by themselves. A portable generator needs someone to fuel it, start it and run cords or flip a transfer switch, in the middle of a storm.

• Battery vs generator: 10-year cost with your state's propane price and your outage hours.
• Battery size for outages: how many kWh you need for your loads and days.
• Portable generator size: the generator that starts your appliances.
• Standby generator cost: what it costs to keep one ready each year.