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Calculators / Batteries and solar

How much home battery do you need?

Start from your electric bill, pick how long you want to ride out an outage and what you’ll keep running. You’ll get the battery size and how many of each brand it takes.

Updated · How we check our numbers

These are example numbers. Put in yours.

Your use

Starting point
kWh

On your bill. EIA’s US average is about 899 kWh a month.

%

All of it, or just the essentials. Skipping AC and the dryer cuts it a lot.

The outage

hours
kW

Add the watts of everything that could run together, ÷ 1,000.

A

LRA on the outdoor unit’s nameplate. Leave blank if no central AC.

You need about

11.8 kWh

1.2 kW average × 24 h × 40% = 11.8 kWh, and 5 kW at once. Smallest fit: 1 × Tesla Powerwall 3.

Energy
11.8 kWh24 hours
Peak
5 kWall at once
Average
1.2 kW899 kWh ÷ 730 h

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

average = 899 kWh a month ÷ 730 h = 1.2 kW

energy = 1.2 kW × 24 h × 40% = 11.8 kWh

units = the larger of energy ÷ usable kWh and peak ÷ continuous kW

How many of each

11.8 kWh, 5 kW
  • Tesla Powerwall 31 × 13.5 kWh = 13.5 kWh, 11.5 kW; starts 185 A LRA per unit
    1 unit
  • Enphase IQ Battery 5P3 × 5 kWh = 15 kWh, 11.5 kW; starts 48 A LRA per unit
    3 units
  • Enphase IQ Battery 10C2 × 10 kWh = 20 kWh, 14.2 kW; starts 90 A LRA per unit
    2 units
  • FranklinWH aPower 21 × 15 kWh = 15 kWh, 10 kW; starts 185 A LRA per unit
    1 unit
  • LG ESS Home 81 × 14.4 kWh = 14.4 kWh, 7.5 kW
    1 unit
  • SolarEdge Home Battery 400V2 × 9.7 kWh = 19.4 kWh, 10 kW
    2 units
  • sonnenCore+ (10 kWh)2 × 10 kWh = 20 kWh, 9.6 kW
    2 units
  • Generac PWRcell 212 kWh configuration, 7 kW, AC start 87 A
    12 kWh

Usable kWh and continuous kW from each datasheet. Installers size to your panel and solar too.

The peak matters as much as the energy

Batteries limit how much can run at once (continuous kW) as well as for how long (kWh). Add up what you’d run together: a fridge, lights, a well pump, a furnace blower. Central AC and well pumps also need a surge to start; compare the LRA on the unit’s nameplate with the battery’s rating.

Central AC?

Put in the LRA (locked-rotor amps) from your AC’s outdoor unit nameplate to check whether one battery can start it: Enphase 5P 48 A, 10C 90 A, FranklinWH aPower 2 185 A, PWRcell 2 65 to 130 A.

No federal credit in 2026

The residential clean energy credit, which covered batteries of 3 kWh or more, ends for property installed after December 31, 2025 (IRS).

How we work it out

energy (kWh) = average kW × hours × share kept running

Your bill gives monthly kWh; divide by 730, the hours in an average month, for your average load. Then pick how much of it you'll keep running: a whole house with AC needs far more than a fridge, lights, internet and a furnace blower.

units = the larger of energy ÷ usable kWh and peak kW ÷ continuous kW

A battery has two limits: how much it stores and how much it can deliver at once. We check both against each maker's datasheet: Enphase IQ 5P (5 kWh, 3.84 kVA), IQ 10C (10 kWh, 7.08 kVA), FranklinWH aPower 2 (15 kWh, 10 kW), LG ESS Home 8 (14.4 kWh, 7.5 kVA), SolarEdge Home Battery 400V (9.7 kWh, 5 kW, 7.5 kW for 10 seconds), sonnenCore+ (10 kWh, 4.8 kVA) and Generac PWRcell 2 in its fixed sizes.

Central AC needs a big surge to start. Its outdoor unit lists locked-rotor amps (LRA); Enphase rates the 5P to start up to 48 A LRA and the 10C up to 90 A, FranklinWH the aPower 2 to 185 A, and Generac gives 65 to 130 A by size.

Where the numbers come from

Guides

Power

Running cost

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