A whole house battery backup system is a fixed home battery paired with an inverter and a transfer gateway that keeps part or all of your home powered during an outage.
Utility power drops, the gateway switches your house onto stored DC electricity, and the inverter converts it to AC for your outlets. That whole sequence happens automatically, usually in under a second, which is why the lights flicker instead of dying. The catch most buyers learn after signing: “whole house” does not always mean every circuit. Whether your air conditioner, well pump, and electric range ride through an outage depends on load size, the backup panel design, and how your installer configures the system.
How a Whole House Battery Backup System Works
Four parts do the work: the battery stack, an inverter that converts DC to AC, a backup gateway or transfer switch that isolates you from the grid, and load management software that decides what gets power.
Both run on lithium chemistry and both are designed for daily use, not just emergencies: they store cheap overnight or solar power and discharge it during peak utility rates, so the hardware pays part of its own cost back before an outage ever happens.
Capacity (kWh) and power (kW) are two different numbers, and mixing them up is the most common buying mistake. Capacity decides how long you can run. Power decides what you can start.
Can It Actually Power Your Entire House?
Rarely every circuit at once. Whole-home coverage depends on the home’s peak load, the starting surge of big appliances, and the installed backup architecture.
If the combined peak exceeds the inverter’s output, the installer wires a backup subpanel instead — powering the fridge, furnace blower, internet, lights, and a few outlets while leaving the AC and electric range on the grid.
Generac’s modular design targets this with 3 to 6 modules per cabinet, so a smaller starting setup can be expanded later rather than replaced. Either way, ask your installer for the load calculation sheet in writing. It shows exactly which breakers sit on backup power, and it is the only reliable answer for your specific house.
| System | Capacity & Power | Installed Cost Range |
|---|---|---|
| Tesla Powerwall 3 | 13.5 kWh; 11.5 kW continuous and peak; integrated inverter | From $9,300 per unit before installation and incentives |
| Tesla Powerwall 2 | 13.5 kWh usable; 5 kW continuous / 7 kW peak | $7,500 battery only; roughly $12,000–$16,500 installed |
| Generac PWRcell | 9–18 kWh usable per cabinet; 3–6 modules | About $12,000–$20,000; battery floor near $12,500 |
| Typical protected loads | Fridge, furnace blower, lights, internet, sump pump | Included in design, not billed separately |
| Not protected above output | Central AC, electric range, EV charger | Needs load management or grid fallback |
| Installation | Licensed electrician, permit, utility interconnection | Labor varies by region and panel work |
| Coupling | AC-coupled or DC-coupled to existing solar | Affects retrofit complexity and cost |
What These Systems Cost and What Changes the Price
Quote ranges swing by thousands for identical hardware, because the hardware is only part of the invoice. Installation, permits, panel work, and utility interconnection rules do the rest.
Treat those as planning benchmarks, never as quotes — regional labor rates and whether solar is included move the total substantially.
Installation is not a weekend project either. Tesla’s own material states installation by a trained electrician is required, and most jurisdictions add a permit plus a utility interconnection application on top. If you are already comparing hardware, a tested whole-house battery backup roundup can shortcut the spec-sheet comparison before you call installers.
One more distinction worth keeping straight: these are fixed residential storage systems with permanent inverter and transfer equipment. They are not portable power stations and not generators, even though all three get marketed as “backup power.”
What to Verify Before You Buy
Confirm three things in writing: the load calculation, the battery’s power output versus your surge loads, and the current spec sheet for your exact model. Published specifications change between product generations, so verify operating temperature limits, enclosure ratings, and code-compliant placement directly with the manufacturer and your installer before signing.
Look at the Powerwall 3 technical review for the 13.5 kWh, 11.5 kW figures cited above, and compare modular options through EnergySage’s PWRcell review. Generac’s own PWRcell 2 sell sheet is the primary source for the modular cabinet layout.
FAQs
How long will a home battery run my house during an outage?
Runtime depends on how much you draw, not just how much the battery stores. Add central AC or an electric range and the same battery drains in a few hours.
Can I add a battery to my existing solar panels?
Usually yes, but the coupling type matters. AC-coupled systems retrofit more easily onto existing solar inverters, while DC-coupled designs can be more efficient in new builds. Your installer needs to confirm compatibility with your current inverter and backup panel before quoting the job.
Is a home battery the same as a generator?
No. A battery stores and silently discharges electricity with no fuel, exhaust, or moving parts, but its runtime is finite and tied to capacity.
References & Sources
- Clean Energy Reviews. “Tesla Powerwall 3 Review.” Source for Powerwall 3 capacity, power output, and reported pricing.
- EnergySage. “Generac PWRcell Battery Review.” Source for PWRcell modular capacity and installed cost ranges.
- Generac. “PWRcell 2 Sell Sheet.” Manufacturer material on the modular cabinet configuration.
