Battery Education · Sizing & Runtime
How Long Does
Battery Backup Last?
The honest answer depends on what you're running. Here's the complete breakdown — appliance-by-appliance load calculations, Powerwall runtime estimates, and how solar recharging changes everything for Fresno homeowners.
The Math: kWh Capacity ÷ Load = Runtime
Battery runtime is simple math: divide the battery's usable capacity (in kWh) by your load (in kW). A Tesla Powerwall 3 has 13.5 kWh of usable capacity. If you're running 1 kW of loads, it lasts 13.5 hours. If you're running 3 kW, it lasts 4.5 hours.
The key variable is what you choose to run. Most homeowners have two modes: "essential loads only" (refrigerator, lights, outlets, medical equipment) and "whole-home backup" (everything including AC). The difference in runtime is dramatic.
Recommended baseline
Essential Loads Only
Most common setup
Essential + Comfort
Requires 2+ batteries
Whole Home (with AC)
Appliance Load Reference Table
Use this table to estimate your backup load. Add up the watts of everything you want to run, then divide your battery capacity by that number to get runtime in hours.
| Appliance | Running Watts | Daily kWh | Priority |
|---|---|---|---|
| Refrigerator (modern) | 100–150W | 2–4 kWh | Essential |
| LED lighting (whole home) | 100–300W | 1–3 kWh | Essential |
| Router + modem | 15–25W | 0.4–0.6 kWh | Essential |
| Phone charging (4 phones) | 20–40W | 0.5–1 kWh | Essential |
| CPAP machine | 30–60W | 0.7–1.4 kWh | Essential |
| Laptop computers (2) | 60–120W | 1–3 kWh | Comfort |
| Television (65") | 100–150W | 0.5–1.5 kWh | Comfort |
| Window AC (5,000 BTU) | 500W | 6–10 kWh | Comfort |
| Microwave (intermittent) | 1,000–1,500W | 0.5–1 kWh | Comfort |
| Central AC (3-ton) | 3,000–4,000W | 24–40 kWh | Heavy |
| Electric water heater | 4,000–5,500W | 10–15 kWh | Heavy |
| Electric clothes dryer | 5,000–6,000W | 3–5 kWh/load | Heavy |
| Electric range (one burner) | 1,200–2,400W | Variable | Heavy |
Why Solar + Battery Is the Right Answer for Fresno
Without solar, a home battery is a finite resource. A single Powerwall 3 (13.5 kWh) running essential loads will last 24–36 hours — enough for a typical overnight outage, but not for a 3-day PSPS event.
With solar, the math changes completely. A 7 kW solar system in Fresno generates approximately 35–40 kWh per day in summer. That's enough to recharge a Powerwall 3 nearly three times over in a single day. During a multi-day PSPS event, your battery recharges every day from your panels — giving you indefinite backup capability for essential loads.
The Fresno PSPS Reality
PG&E has shut off power to parts of Fresno County multiple times during high-wind fire weather events. The 2019 PSPS events lasted 2–5 days in some areas. A battery-only system (no solar) would be depleted after day 1. A solar + battery system runs indefinitely.
Frequently Asked Questions
How long can a Tesla Powerwall power a house in Fresno?
A single Tesla Powerwall 3 (13.5 kWh) can power essential loads (refrigerator, lights, outlets, router) for 24–36 hours without solar recharging. With solar recharging, it can run indefinitely. For whole-home backup including central air conditioning, two Powerwalls (27 kWh) are recommended for Fresno's summer heat.
Can a home battery run air conditioning during a Fresno outage?
Yes, but it requires proper sizing. A 3-ton central AC unit draws approximately 3,500W. A single Powerwall 3 (13.5 kWh) can run it for about 3–4 hours. Two Powerwalls can run it for 6–8 hours. With solar recharging during the day, you can run AC during daylight hours and rely on stored energy at night.
What appliances can a home battery backup run?
A properly configured battery backup system can run any appliance in your home, subject to capacity limits. Essential loads (refrigerator, lights, outlets, router, medical equipment) can run for 24+ hours on a single Powerwall. Heavy loads (AC, electric range, water heater) require larger battery capacity or load management.
How many kWh does a Fresno home use per day?
The average Fresno home uses 30–50 kWh per day, with summer peaks of 60–80 kWh on hot days when AC runs continuously. Essential loads (without AC) typically total 8–15 kWh per day. This is why whole-home backup requires multiple battery units or solar recharging.
Does a home battery recharge during a power outage?
Yes — if you have solar panels. During a grid outage, your solar panels continue to generate power and recharge the battery. This is what makes solar + battery the most powerful combination for Central Valley homeowners: the battery recharges every day, giving you indefinite backup capability for essential loads.
How many batteries do I need for whole-home backup in Fresno?
For whole-home backup including central air conditioning in Fresno's summer heat, we typically recommend 2–3 Powerwall 3 units (27–40.5 kWh) or equivalent capacity from other brands. For essential loads only (no AC), one Powerwall 3 is usually sufficient with solar recharging.
Find Out How Much Backup You Need
We size battery systems based on your actual energy usage and backup goals. Free assessment in Fresno, Clovis, Madera, and 70+ Central Valley communities. Licensed contractor #1063682.
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