Battery Backup for Power Outages: Plan the Kit Before the Grid Drops
Match a battery to your actual outage profile — blip, overnight, or multi-day — with the load math written out, a plug-in priority list, and the recharge strategies that stretch one battery across a long outage.
The mistake people make with backup power is planning for the hurricane on the news instead of the outage they actually get. Your grid history — not the worst case — should size the battery. A portable power station (a solar generator, once panels enter the plan) covers the overwhelming majority of US outages with room to spare; the arithmetic below shows where that stops being true and what to do about it.
What outage are you actually planning for?
Three profiles cover nearly everyone. Work out which one is yours before spending anything.
| Outage profile | Duration | Essentials energy needed | Battery class |
|---|---|---|---|
| The blip | Minutes to ~2 hours | ≤ 200 Wh | Anything — even a 256 Wh unit |
| The overnight | 4–14 hours | ~400–1,300 Wh | 1 kWh class |
| The event | 1–3+ days | 2,600 Wh/day and up | 2–3.6 kWh + expansion or solar |
The essentials figure behind that table — fridge, router, LED lights, laptop,
CPAP, two phones — totals about 2,192 Wh per day, derived line by line in
our home backup guide. One
day of it needs 2,192 ÷ 0.85 ≈ 2,600 Wh of rated battery after inverter
losses. An overnight outage is roughly half a day’s worth, which is why the
1 kWh class — about 850 usable Wh — is the sweet spot for most households:
it runs the fridge and comms from dinner to breakfast (1,024 × 0.85 ÷ 2,192
× 24 ≈ 9.5 hours).
If your profile is “the event,” stop shopping for a single box. No portable unit stores three days of essentials; that job goes to expansion batteries or solar recharge, sized in the home battery backup guide.
Two worked examples
A two-person apartment, overnight outage risk. Router (15 W × 24 h = 360 Wh), compact fridge (28 W average × 24 h = 672 Wh), two phones (40 Wh), a lamp or two (80 Wh) — about 1,150 Wh per day, or roughly 575 Wh for an overnight. At 85% efficiency that’s ~680 Wh of rated battery: the 1 kWh class covers it with margin to spare, and even a 288 Wh unit protects the phones and router through the evening.
A family house with a CPAP, multi-day storm risk. The full essentials table applies — 2,192 Wh per day — and the planning question becomes days, not devices: two days is 5,200 Wh of rated battery, which no single portable unit stores. The workable configurations are a 2–3.6 kWh base with expansion batteries, or the same base plus 400+ W of solar for recovery between storm fronts. Both are priced and compared in the home battery backup guide.
Your household sits somewhere between these two — the calculator turns your actual device list into the same arithmetic.
What gets power first?
When the outage arrives, plug in by priority rather than by proximity:
- Medical loads. CPAP, oxygen concentrator, refrigerated medication. These come first and their arithmetic is friendly — a 40 W CPAP with the humidifier off is just 320 Wh per 8-hour night. Our CPAP guide covers the details.
- The refrigerator. The biggest steady load and the one with a deadline — details in the next section.
- Communications. Router and modem (~15 W combined) keep phones on Wi-Fi, outage maps reachable, and phone batteries out of the equation.
- Lights, then everything else. A few LED lamps at 5–8 W each cost almost nothing — five hours of evening light from three lamps is under 120 Wh, a rounding error next to the fridge.
And the exclusion list, which matters more than the priority list: nothing with a heating element. An electric kettle at 1,500 W burns an entire 1 kWh battery in about 34 minutes (1,024 × 0.85 ÷ 1,500 ≈ 0.57 h). Kettles, space heaters, toasters, hair dryers — during an outage they are all luxury items priced in fridge-hours.
The refrigerator: your main load and your main deadline
The fridge dominates outage planning because it’s both the largest essential load and the one attached to a food-safety clock. The numbers, from our fridge runtime guide: a household fridge averages 48 W duty-cycled — about 1,152 Wh/day — so a 1,024 Wh unit runs it roughly 18 hours straight (1,024 × 0.85 ÷ 48 ≈ 18.1 — budget less in practice for door openings), and a 2,048 Wh unit about 36 hours.
You also have more margin than the runtime alone suggests: an unopened fridge holds safe temperatures for about 4 hours on its own, and a full freezer for about 48. Powering the fridge in alternating blocks — a few hours on, an unopened hour off — stretches battery coverage well past the straight-line figure when you’re rationing watt-hours in a long outage.
A battery you can refill beats a bigger battery
Past the first day, recharge strategy matters more than capacity. Three options, in ascending effectiveness:
- A car’s 12V outlet delivers roughly 100 W — slow, but an overnight idle or a supply run adds several hundred watt-hours.
- Solar panels are the sustainable answer: a 400 W array realistically returns 1,200–1,600 Wh on a clear day (plan on 60–70% of sticker rating), most of an essentials day. The catch is that grid-down weather is often panel-down weather — treat solar as recovery between storm fronts, not guaranteed daily income.
- Any AC source for one hour. Modern fast-charging units make this the killer feature: an EcoFlow DELTA 3 refills 0–100% in about 56 minutes. A neighbor with power, a workplace outlet, or a gas generator run for a single fuel-sipping hour resets your whole day. This is the logic of the battery-plus-generator pairing in our power station vs gas generator comparison.
What about medical devices during an outage?
If a CPAP, oxygen concentrator, or refrigerated medication is the reason you’re reading this, size for it first and let everything else share the remainder. The good news is that CPAP arithmetic is friendly: a typical machine draws about 40 W with the heated humidifier off, so one 8-hour night costs 320 Wh — meaning even a 1 kWh unit holds two full nights of therapy plus several fridge-hours (870 usable Wh − 640 Wh of CPAP ≈ 4 fridge-hours at 48 W). The humidifier is the trap: heated humidification and tube heating can triple the draw, which is why every outage plan for CPAP users starts with “run it dry.” Oxygen concentrators are a different class of problem — 300 W and up, continuously — and need the 2 kWh class as a floor plus a firm recharge plan. The CPAP guide works both cases in detail, including the DC-supply trick that roughly halves overnight CPAP consumption.
Is a UPS good enough instead?
A computer-style UPS and a portable power station solve different outages, and the difference is two orders of magnitude. A typical desktop UPS stores 50–150 Wh and exists to give you minutes: enough to save work and shut down cleanly, or to ride through a blip. Against a real outage it’s a rounding error — 150 Wh is about three hours of fridge duty (150 ÷ 48) even before its always-on inverter losses, which are proportionally much higher than a power station’s. What the UPS does better is switchover: it cuts over in milliseconds without your involvement, which is why servers and desktops use them. The practical pairing for a home office is both: the UPS bridges the first thirty seconds, then you move the router and laptop onto the power station for the duration. If you only buy one and your concern is outages rather than crashes, buy the power station.
Before the outage: the ten-minute setup
A backup battery only works as well as its standby routine. Keep it charged — LiFePO4 chemistry holds charge for months and tolerates sitting at 100%, and an outage that starts at 40% halves every number on this page. Keep it findable, with the cables it needs, near the fridge it will serve. And run the drill once: power the fridge from it for an afternoon. You’ll learn your fridge’s real draw, confirm the compressor’s startup surge doesn’t trip the inverter, and discover any missing cable on a calm Saturday instead of at hour one of a storm. Size against your own device list with the calculator, and if hurricanes are your outage profile, work through the hurricane season checklist.
Related
- Best home battery backup — which unit to buy, portable vs installed
- How long will a power station run a fridge? — the load that decides your capacity class
- Best solar generator for home backup — the full essentials-load derivation
- Hurricane season power checklist — the seasonal version of this page
Food-safety windows (4 hours refrigerated, 48 hours full freezer) follow USDA guidance for unopened appliances. All prices referenced are MSRP.
Frequently asked questions
- What is the best battery backup for a power outage?
- Match it to your typical outage. For blips and evenings, a 1 kWh portable power station (≈850 usable Wh at 85% inverter efficiency) runs a fridge, router, lights and phones through the night. For day-long outages, the 2 kWh class covers about 19 hours of essentials. For multi-day events you need expansion batteries or solar input — no single portable unit stores three days of household essentials.
- How long will a battery backup last during a power outage?
- Usable capacity divided by load. Household essentials — fridge, router, lights, laptop, CPAP, phones — draw about 2,200 Wh per day, so a 1,024 Wh unit lasts roughly 9½ hours of full essentials duty, a 2,048 Wh unit about 19 hours, and a 3,600 Wh unit about 33 hours. Cut the load list in half and every number doubles.
- What should I plug into a battery backup first during an outage?
- In order: medical devices (CPAP, oxygen concentrator, powered medication cooling), then the refrigerator, then communications — router, modem, and phones — then lights. Skip electric kettles, space heaters, toasters and hair dryers entirely: any heating element drains a battery ten to thirty times faster than the essentials and most exceed small inverters anyway.
- Can a battery backup keep a refrigerator running through an outage?
- Yes — this is the core job. A household fridge averages about 48 W once its compressor duty cycle is counted, roughly 1,150 Wh per day. A 1,024 Wh power station runs it about 18 hours; a 2 kWh unit about 36 hours. The fridge itself buys you margin: unopened, it holds safe temperatures for about 4 hours, so duty-cycling the battery — powered hours alternating with unopened hours — stretches runtime further.
- How do you recharge a power station when the power is out?
- Three ways: solar panels (a 400 W array returns roughly 1,200–1,600 Wh on a clear day — half to three-quarters of an essentials day), a car's 12V outlet (slow, ~100 W, but meaningful overnight), or an hour of a neighbor's or a gas generator's AC power — fast-charging units refill in about an hour. A battery with a recharge plan outlasts a bigger battery without one.