What Can a Home Battery Power? Choosing Your Backup Loads
A home battery cannot power everything indefinitely — but the right load selection keeps your most important appliances running through a blackout.
When a blackout hits, a home battery does not automatically power your entire house. Most residential systems are designed to back up selected circuits — the appliances and outlets you pre-select during installation. Choosing those loads wisely determines whether your battery lasts hours or days.
Backup Load Tiers
| Priority | Tier | Typical examples |
|---|---|---|
| Essential — always backed up | Tier 1 | Fridge/freezer, lighting, phone chargers, Wi-Fi router, medical devices |
| Common additions | Tier 2 | Microwave, television, laptops, security cameras |
| Consider carefully | Tier 3 | Split system AC, well or pressure pump, chest freezer |
| Rarely backed up | Tier 4 | EV charger, electric dryer, electric oven, electric hot water system |
Why Not Back Up Everything?
- Cost — whole-home backup requires significantly more battery capacity, raising installation cost sharply
- Capacity — a 10 kWh battery depleted in 2 hours by high-draw appliances gives you no overnight coverage
- Surge power — motors like split system compressors draw 3–5× their running wattage at startup
- Energy hierarchy — a fridge protecting food over three days is more valuable than one hour of air conditioning
Estimated Runtimes
These estimates assume baseline loads: fridge, Wi-Fi, phone chargers, some lighting, television and two laptops.
| Battery size | Loads | Sunny day | Cloudy day (no solar top-up) |
|---|---|---|---|
| 10 kWh | Essentials only | 7+ days | 36–48 hours |
| 10 kWh | Essentials + split system AC | 7+ days | 6–10 hours |
| 20 kWh | Essentials only | 7+ days | 72+ hours |
| 20 kWh | Essentials + split system AC | 7+ days | 14–20 hours |
The single biggest decision: include or exclude your split system air conditioner. Dropping it from a 10 kWh system can multiply cloudy-day runtime from 8 hours to two days.
Plan Before You Install
Backup load selection should be decided during the installation design phase, not after. Adding circuits to a backup system post-installation requires a licensed electrician to run additional wiring — it is easier and cheaper to plan upfront. Ask your installer to walk through each circuit in your switchboard and help you prioritise.