How to Choose a Home Battery for Power Outages: 7 Specs That Matter

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Home battery spec sheets are full of numbers, and the biggest one on the box is rarely the one that decides whether your house stays comfortable in an outage. This guide explains the seven specs that matter for backup, in the order we would check them, with real figures from manufacturer spec pages so you can see how products differ.

WattFortress has not lab-tested these products. Specs below were taken from the manufacturers' pages on October 17, 2026 (the same check our buyer's guide uses). Always confirm current specs on the seller's site before buying.

Two kinds of "home battery"

• Large power stations (for example EcoFlow DELTA Pro 3, Jackery Explorer 5000 Plus, Anker SOLIX F3800 Plus, BLUETTI AC500): an inverter and battery in one or two boxes with outlets on the front. They can run appliances by cord on day one, and many connect to a transfer switch or smart panel later.
• Installed wall or floor batteries (for example Tesla Powerwall 3): permanently wired into your electrical service by an installer, usually alongside solar.

Either can be a good outage battery. The specs below apply to both.

1. Usable energy (kWh): how long

Capacity in watt-hours (Wh) or kilowatt-hours (kWh) sets how long the battery lasts. Check whether the figure is DC battery capacity or AC energy delivered. Tesla lists Powerwall 3 at 13.5 kWh of AC energy on its datasheet; power stations usually list DC battery capacity, and you lose some of that in the inverter.

Our planning rule for DC-rated units: usable AC energy ≈ rated Wh × 0.90 (usable) × 0.85 (inverter). Both factors are WattFortress assumptions. For a 5,040Wh unit that is about 3,856Wh.

To size it, add up the energy your must-run loads use per day. Our How many kWh of battery do you need for whole-home backup? guide has worked examples.

2. Continuous output (W): how much at once

This is how many watts the inverter can deliver indefinitely. Add up everything that might run at the same time. Published figures range widely:

3. Surge: can it start your motors?

Motors draw several times their running watts for a moment. Champion Power Equipment's chart lists, as typical ranges, a 1 HP well pump at 1,000-2,000W running and 2,000-4,000W starting, and a 3-ton central AC at 3,000-3,500W running and 5,000-6,000W starting (checked Nov 1, 2026). Compare your largest motor's startup (plus everything else running) against the surge rating. If a surge figure isn't published, ask the manufacturer before counting on it.

4. 120V only, or 120/240V?

Well pumps, many central AC units, electric dryers and some furnaces need 240V. If you have any 240V load you must run, filter for units with 240V output (the DELTA Pro 3, Jackery 5000 Plus, F3800 Plus and DELTA Pro Ultra X all list it) and read the fine print. For example, EcoFlow says the DELTA Pro 3's 120V and 240V outlet groups cannot both be on at once. Our Power station for a 240V well pump guide goes deeper.

5. Expandability

Outage needs grow once you see how useful backup is. Published maximums differ a lot: DELTA Pro 3 up to 12 kWh per unit, Jackery 5000 Plus up to 30 kWh per unit, F3800 Plus up to 53.8 kWh in a two-unit system, AC500 up to 18,432Wh with six B300S batteries, and DELTA Pro Ultra X up to 61.44 kWh per inverter. Buying a unit that can add batteries later is often cheaper than replacing it.

6. Solar input: recharging in a long outage

If outages last days, recharging matters as much as capacity. Check the PV input's voltage window, current limit and maximum watts. They vary from low-voltage ports (Anker F3800 base model: 11-60V) to high-voltage inputs (DELTA Pro Ultra X: two 80-500V inputs, 5,000W each). Our solar sizing and series-panel guides explain how to match panels to those limits.

7. Switchover (UPS) time and home integration

If the battery sits between the grid and your loads, switchover time decides whether sensitive electronics notice the outage. Manufacturers list, for example, 10ms for the DELTA Pro 3 and 20ms for the AC500; Jackery lists an online UPS mode at 0ms. For whole-circuit backup, check which transfer switch or smart panel the product supports. Anything wired into your panel must be installed by a licensed electrician, with permits, following the National Electrical Code (NFPA 70) and your local rules.

Specs that matter less than they look

• Number of outlets. Useful, but you can add a power strip; you cannot add surge capacity.
• Peak charging speed from the wall. Nice for convenience; during an outage there is no wall.
• Marketing "up to" figures. Look for the number in the spec table, not the headline.

A quick decision checklist

1. List must-run loads and their daily Wh.
2. Find the largest motor and its startup watts.
3. Note any 240V loads.
4. Decide how many hours or days you need without recharging.
5. Filter by continuous output, surge and voltage, then by capacity and expansion.
6. If outages run longer than your battery, size solar input next.
7. Confirm price, warranty and current specs on the seller's site.

FAQ

Is a bigger battery always better? Only if your inverter can also deliver the power you need. A huge battery behind a small inverter can still trip on a well pump start.

Do I need solar to use a home battery? No. You can charge from the grid and hold it in reserve. Solar extends runtime in long outages.

Should I choose LFP chemistry? All the power stations above list LFP (LiFePO4) batteries. Compare cycle ratings carefully; manufacturers use different end-of-life percentages.

Product links: Check price at EcoFlow EcoFlow DELTA Pro 3 · Check price at Jackery Jackery Explorer 5000 Plus · Check price at Anker SOLIX Anker SOLIX F3800 Plus · Check price BLUETTI AC500 · Check price at EcoFlow EcoFlow DELTA Pro Ultra X · Tesla Powerwall 3

DIY battery and inverter parts: Shop batteries at A1 SolarStore · Shop lithium batteries at Eco-Worthy