Batteries in cold weather

Why your battery may charge more slowly, or hold less, when it is very cold, and what helps.

Home batteries use lithium cells, which don't like being very cold. On cold days your battery may charge more slowly, or hold a little less, to protect itself. This is normal, and it recovers as the battery warms up.

What changes when it's cold

Below about 10°C, batteries become a little less efficient.
Close to freezing, they hold and deliver noticeably less, and charging is slowed or stopped to protect the cells.
These limits are about the temperature inside the battery, not the air. A battery that has been sitting idle overnight stays cold for longer.

By make

Your battery	What it does in the cold
Tesla Powerwall 3	Charging is limited between 0°C and 10°C, and stops below 0°C (cell temperature). Heat Mode, standard since late 2023, keeps the cells above freezing and warms them ahead of sunrise. A full Powerwall may let itself get colder, because it doesn't need to charge.
Tesla Powerwall 2	Warms itself using heat from its own electronics.
Duracell Energy	May charge more slowly when it's cold, to protect the cells.
Fox ESS EP6 / EP12	Rated for indoors or outdoors. A heater option protects them in cold weather.

What helps

A cheap overnight charge. On winter nights, a scheduled grid charge on an off-peak tariff gets the battery working and fills it before the day. See Battery Optimisation Guide: Charging on Off-Peak Tariffs.
Patience on frosty mornings. Charging picks up as the battery warms.
Not changing settings to force it. The battery is protecting itself.

When to contact us

It hasn't charged at all for several days in mild weather.
The app shows a battery error or alarm.
The battery feels hot, looks swollen, or smells of burning. Keep away from it, and if there's smoke or fire, get out and call 999.