Battery storageWhole-home backup
Whole-home battery backup, sized honestly
“Whole-home backup” is the most oversold phrase in home energy. The truth is arithmetic: what you back up determines how many batteries you need, and air conditioning is where most quotes quietly lie. Here's the real sizing math.
The sizing table nobody shows you
| Backup goal | Realistic battery count | What that actually covers |
|---|---|---|
| Essential loads | 1 battery (13.5 kWh) | Fridge, internet, lights, phones, garage door, well/sump pump — typically 2–3 days of runtime, indefinitely with solar recharge |
| Essentials + one big load | 1–2 batteries | Add a well pump cycling hard, an electric range, or limited EV top-ups — runtime drops fast; a load calc decides one vs two |
| Whole-home, no AC in outage | 2 batteries (27 kWh) | Everything runs except you agree to skip air conditioning during an outage — the most popular honest compromise |
| Whole-home including AC | 2–3 batteries + load mgmt | Central AC draws 3–5 kW running with brutal start surges; covering it through a multi-day summer outage is a 2–3 unit design with smart load control |
Assumes Powerwall 3-class units (13.5 kWh usable, ~11.5 kW continuous) with solar recharging during daylight. Your panel capacity matters too — whole-home designs sometimes need a main-panel upgrade or smart load controller, which we price in up front.
What whole-home battery backup costs.
The price follows the sizing table above, because whole-home backup is a two-battery design for most Southern California homes. These are the gross installed prices Helios quotes in 2026, before any incentive, with permit, interconnection and the backup tie-in included:
- One Tesla Powerwall 3: $14,500–$18,500 — an essential-loads design, not whole-home.
- Two Powerwall 3: $24,000–$30,000 — whole-home with air conditioning limited during an outage; the most common honest design.
- One Enphase IQ Battery 10C: $13,000–$15,500; one FranklinWH aPower 2: $16,000–$21,000. A second unit of either adds roughly the battery-only cost, since the controller, permit and crew are shared.
- Main panel upgrade, if the house needs one: $3,000–$5,000.
No federal tax credit applies to a battery purchased in 2026; the prepaid lease passes about 30% of the commercial credit through, and the financing page explains how. For the per-unit breakdown and what moves it, see the Powerwall 3 cost page; for the other two batteries, Enphase battery cost and FranklinWH. Every quote is one all-in written number with the equipment named by model.
The AC reality check.
Air conditioning is the fork in every backup conversation. Power isn't the issue — a single Powerwall 3 can run a central AC. Energy is: at 3–5 kW of draw, AC consumes a full battery in three to four hours, which is why “whole-home backup” quotes built on one unit are really “whole-home until the afternoon” quotes. The honest designs are: skip AC during outages (two units cover everything else for days), or commit to the 2–3 unit + load-management architecture that genuinely carries AC through a summer PSPS event with solar recharging the bank daily. We model your actual loads — including the AC's nameplate draw — and show runtime for each design before you pick one.
Pricing per unit: Powerwall 3 cost breakdown · Utility fit: SCE, SDG&E, LADWP · Rebates: 2026 incentives
Whole-home backup questions, answered.
- How much does a whole home battery backup cost?
- For a Southern California home, whole-home battery backup usually means two batteries. Helios quotes one Tesla Powerwall 3 at $14,500–$18,500 installed and two at $24,000–$30,000, gross, before any incentive; one Enphase IQ Battery 10C runs $13,000–$15,500 and one FranklinWH aPower 2 $16,000–$21,000, with a second unit of either adding roughly the battery-only cost. A main panel upgrade, when the house needs one, adds $3,000–$5,000. There is no federal tax credit for a purchased battery in 2026; the prepaid lease passes about 30% through. You get one all-in written price with the equipment named by model.
- How many Powerwalls do I need for whole-home backup?
- For most SoCal homes: two units (27 kWh) covers whole-home if you exclude or limit air conditioning during outages; running central AC through a multi-day outage honestly takes two to three units plus load management. One unit is an essential-loads design, not whole-home — anyone selling "whole-home backup" on a single battery is defining "whole home" creatively. We run the load calculation before quoting a count.
- Can a Powerwall run my air conditioner?
- Running it, usually yes — one Powerwall 3 outputs ~11.5 kW continuous, and a typical central AC draws 3–5 kW once running (soft-start hardware tames the startup surge). The problem is energy, not power: AC at 4 kW empties a 13.5 kWh battery in under four hours. That's why AC-through-outage designs are multi-unit with daytime solar recharge, and why the honest alternative is backing up everything except AC.
- Battery backup vs. a standby generator — which should I get?
- Batteries win on daily value (they earn money shifting solar into the 4–9 PM peak every day — a generator earns nothing until the grid fails), silence, zero fuel, instant transfer, and no maintenance. Generators win on unlimited runtime for very long outages and heavy loads, at the cost of fuel, noise, upkeep, and permits of their own. For most SoCal solar homes the battery is the right first purchase; rural properties with well pumps and week-long outage exposure sometimes justify both.
- What loads get dropped in an essential-loads design?
- You choose, via a critical-loads panel or smart load controller: typically AC, electric dryer, oven, pool equipment, and EV charging wait out the outage, while refrigeration, lighting, internet, medical devices, and pumps stay live. Smart controllers (including FranklinWH's and Tesla's software controls) can shed loads dynamically instead of hard-wiring the split — the modern approach we usually recommend.