The right battery backup system is sized to the circuits you need during an outage, not to the whole house. List your critical loads, add up how much power they draw and for how long, and then choose a battery capacity and an inverter output that carry them. In Arizona, air conditioning is the deciding factor: include it and the system grows a lot.
What should stay on during an outage?
Start with a short list. Most Arizona homeowners choose:
- the refrigerator and any freezer
- a well pump or booster pump on rural property
- medical equipment such as a CPAP or oxygen concentrator
- lights, outlets for phones, and the Wi-Fi
- ceiling fans, or one cool room with a solar mini split
How do battery capacity and inverter output differ?
| Number | What it decides | What drives it |
|---|---|---|
| Battery capacity | How long your loads run | Your loads and the hours you want covered |
| Inverter output | How much runs at once | The largest loads, and motor starting surge |
| Charging source | How the battery refills | Solar, the grid, or a generator plug-in |
Capacity is the size of the tank. Output is the size of the pipe. A large battery behind a small inverter cannot start a well pump, and a large inverter in front of a small battery runs out quickly.
Partial home or whole home?
A partial home system puts your critical circuits on a dedicated panel. It is the most common choice because it protects what matters without sizing for central air. A whole home system carries the full service, air conditioning included, and is sized around summer peaks. Read more about both on our home battery backup page.
Does Arizona heat change the design?
Yes. Heat shortens battery life, so where the battery lives matters as much as its size. A shaded garage wall or a ventilated utility room is usually better than a west-facing exterior wall.
Ready for a number of your own? Use Build & Price and a licensed electrician will size a system around your list.
Frequently asked questions
Is a bigger battery always better?
No. A battery sized far beyond your critical loads costs more and sits partly unused. Size it to the circuits you chose and the hours you want covered.
What matters more, battery capacity or inverter output?
Both. Capacity decides how long the loads run; inverter output decides how many can run at once, and whether a well pump or compressor can start.
About the author
The Nirvana Energy Team designs and installs battery backup, off-grid solar and licensed electrical work across Arizona under ROC license 357597, CR-11 Electrical.