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Whole-home or critical-loads battery backup?
Updated October 6, 2026 · using typical appliance wattages and battery datasheet ratings · by Cali Energy
Whole-home or critical-loads backup? Add up the appliances you want to run in an outage. A fridge, lights and internet draw well under 4 kW — a compact battery handles them. Add central AC or a well pump and the surge pushes you toward a high-power battery (like an 11.5 kW Powerwall 3) or two. It’s a power question first, energy second.
✓ Sizes the power your loads need against real 2026 battery classes. See every figure it uses ↓
What do you want to keep on during an outage?
Method: continuous load = the sum of the ticked running watts, compared with datasheet ratings (Enphase IQ Battery 5P 3.84 kVA, 10C 7.08 kVA; FranklinWH aPower 2 10 kW; Tesla Powerwall 3 11.5 kW). Runtime = nameplate kWh less a 10% reserve, divided by that load. The watts are examples; your appliances’ nameplates give the real figures — the U.S. Department of Energy notes the nameplate wattage is the maximum draw, or amps times volts (DOE). Motor start is checked separately, against the LRA on the nameplate. A licensed electrician’s load calculation confirms the design.
The rates and figures this calculator usestap to verify
The tool sums the running and surge watts of the loads you tick, then compares them to typical residential battery power classes. The appliance figures are typical estimates; the battery classes reflect 2026 products.
| Compact | Enphase IQ Battery 5P 3.84 kVA; IQ Battery 10C 7.08 kVA |
| High-power | FranklinWH aPower 2 10 kW; Tesla Powerwall 3 11.5 kW |
| Beyond that | two batteries or a load-managing smart panel |
| Running watts | example figures; motor start is checked against the nameplate LRA |
| Usable energy | nameplate kWh × ~0.90 |
| Continuous power | sum of running watts |
| Motor start | nameplate LRA vs the battery’s rating (Powerwall 3 185 LRA; aPower 2 185 A; IQ 10C up to 90 A; IQ 5P 48 A) |
| Runtime energy | continuous kW × hours vs usable kWh |
The appliance running and surge watts are typical estimates for common household equipment — your exact models vary, especially motor-driven loads (AC, well pump, pool pump) whose startup surge can be several times the running draw. The battery power classes reflect 2026 residential products (a Tesla Powerwall 3 delivers 13.5 kWh at 11.5 kW continuous). Usable energy is estimated at ~90% of nameplate after reserve and losses. This is an idealized full-load estimate; real runtime shifts with load cycling, inverter limits, reserve settings, temperature, battery age and any daytime solar recharge.
Example results you can reproduce
Tick the same loads above to reproduce these — the class depends on continuous and surge power.
| Loads kept on | Roughly needs |
|---|---|
| Fridge + lights + internet | A compact battery (< ~3.8 kW continuous) |
| + Central AC or a well pump | A larger battery class, and the motor’s starting current (LRA) must fit the battery’s rating |
| Whole home incl. EV charging | Two batteries or a load-managing smart panel |
How this calculator works
It adds the running watts of every load you tick to get continuous power and compares that with the continuous ratings of common batteries. Motor loads are flagged for a separate start check: the locked-rotor amps (LRA) on the nameplate against the battery’s rating. If you enter a battery capacity and target hours, it also checks the energy side: continuous kW × hours against ~90% of the battery’s usable kWh. Power first, energy second.
How to read your result
Two things matter: continuous kW (can the battery run everything at once?) and, for motor loads, whether it can start them (the nameplate LRA against the battery’s rating). A set can fit on energy but fail on power — a well pump that runs 30 seconds an hour barely moves the kWh but can spike several kilowatts starting. That’s why the tool leads with power and treats the runtime energy as a secondary check.
What moves the result the most
Motor surge — central AC, well pumps and pool pumps — is by far the biggest driver, often deciding compact vs high-power on its own. After that, the number of loads you keep on (continuous power) and, for runtime, the hours you want and the battery’s usable capacity. EV charging is a special case: at 7–11 kW it can exceed a single battery’s output by itself.
Common questions
What’s the difference between whole-home and critical-loads backup?
Critical-loads backup keeps a few essential circuits alive (fridge, lights, internet) on a compact battery; whole-home backup runs everything, which needs far more power — often a high-power battery or two plus a smart panel.
Why does surge matter so much?
Motors draw several times their running watts for a split second when they start. A battery that easily runs a load can still be unable to start it, so peak (surge) power, not just continuous, sets the requirement.
What’s a compact vs high-power battery?
Compact units deliver roughly 3.8 kW continuous; high-power units like the Powerwall 3 deliver about 11.5 kW, enough to start and run larger loads including many central ACs.
Can one battery back up a whole home?
Sometimes — a high-power battery can run a modest all-electric home, but big or simultaneous motor loads (AC + well pump + EV) usually need two batteries or a smart panel that sheds loads.
How long will the battery last in an outage?
That’s the energy side. Enter your battery capacity and target hours here for a rough check, or size the kWh from scratch with our battery sizing calculator.
Does solar help during an outage?
Yes — a solar-plus-battery system recharges by day, so you can run more loads for longer than the battery alone would allow. A battery-only setup is limited to its stored energy.
Sources
- North Carolina OSFM — Formal interpretation of 2023 NEC 702.4(A)(2): full load or energy management system (December 1, 2024)
- California Building Standards Commission — 2025 Title 24 code changes (California Electrical Code based on the 2023 NEC; effective January 1, 2026)
- Tesla — Powerwall 3 datasheet (13.5 kWh, up to 11.5 kW, 185 LRA; whole-home and partial-home configurations)
- FranklinWH — aPower 2 datasheet (15 kWh, 10 kW / 11.5 kVA, 185 A LRA at 11.5 kVA)
- FranklinWH — aGate X 1.1 datasheet (automatic load shedding, Smart Circuits, 200 A backup load port)
- Enphase — IQ Battery 5P datasheet (5.0 kWh, 3.84 kVA, up to 48 A LRA)
- Enphase — IQ Battery 10C datasheet (10.0 kWh, 7.08 kVA, up to 90 A LRA)
- Enphase — IQ Load Controller datasheet (IQLC-DSH-00022, May 2024)
- U.S. Department of Energy — Estimating appliance and home electronic energy use (nameplate wattage)
Estimates only, not a quote. Assumptions, rates, incentives and program rules can change — confirm current details with your utility, the program administrator or a licensed professional.
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