How Long Will a Solar Battery Last During a Power Outage?

How long will a solar battery last in a power outage?

Honest answer: it depends on two numbers, and anybody who quotes you a flat "X hours" without asking about your home is guessing. Runtime comes down to how much usable energy your battery holds and how fast your home burns through it. Get those two numbers and you can estimate your own backup time.

A single popular home battery holds roughly 13.5 kWh of usable energy. Whether that lasts three hours or thirty is almost entirely about what you choose to run. This post is part of our Central Florida solar battery backup guide.

How do I calculate my battery's runtime?

The math is simple: usable capacity (kWh) ÷ your load (kW) = hours of runtime. So a 13.5 kWh battery powering a steady 1 kW of essentials lasts about 13.5 hours; powering a 4 kW load lasts a bit over 3 hours.

To ballpark your own load, add up what you'd really run:

• Refrigerator: roughly 0.1–0.2 kW average (it cycles on and off)
• LED lights, phones, laptop, Wi-Fi router: a few hundred watts combined
• Ceiling and box fans: around 0.05–0.1 kW each
• Well pump: a big intermittent spike when it kicks on
• Central air conditioning: often 3–5 kW while it's running — the big one

That list is exactly why essentials-only backup stretches for a day or more while a whole-home approach with AC drains fast.

Why does air conditioning drain a battery so fast?

Because central AC is, by a mile, the hungriest thing in a Florida home. A central system can pull 3 to 5 kW every time the compressor runs — more than every light, fan, and phone charger in the house put together. Point a 13.5 kWh battery at that and you can empty it in a few hours.

This is the hard tradeoff of Florida backup: the same storms that cause the outages also bring the heat that makes you want AC most. Plenty of homeowners split the difference with fans and a single mini-split or window unit for one room instead of running central air. Deciding that before the outage is part of good hurricane-season battery prep.

Does the sun recharge my battery during an outage?

Yes — and this is the edge solar-plus-storage has over a plain generator. As long as your system's set up for backup, your panels keep charging the battery during daylight even while the grid is down. In practice you get a daily cycle: the battery carries you through the night, the sun refills it the next day, and you repeat.

That's why a solar battery can outlast a fuel generator in a multi-day outage — no fuel runs, no gas-station lines. The one limit is weather: several storm-darkened days in a row cut how much your panels can put back, so runtime tightens up. Keeping the glass clean helps them recharge as fast as possible.

Does a battery lose runtime as it ages?

It does. Every lithium battery slowly loses usable capacity over years of cycling — the industry term is capacity fade — so a battery that once ran your essentials for a full day may run them a little less as it gets older. Florida's heat speeds that aging up, which is why placement, ventilation, and firmware matter so much here.

The tricky part is that the capacity loss stays invisible until an outage exposes it. A health check measures what your battery can actually deliver today versus its rating — see Central Florida solar battery maintenance. We test battery capacity and backup performance across Kissimmee and all of Central Florida, on any brand of battery — even the ones we didn't install.

👉 Request a free battery health check or call (407) 270-2542.

Frequently asked questions