If you use an old Android phone as a shop or home security camera, it will spend most of its life on a charger. So it is easy to think the battery does not matter.

It matters the moment the power goes out. In a power cut, the phone's own battery is the only thing keeping the camera recording. In places where power cuts are a normal part of the week, the battery is the camera's backup power supply, and an old phone's battery may be much weaker than it looks.

This guide shows how to check an old phone's battery before you give it camera duty, using only what is already on the phone or free from the phone's maker. No battery app to buy, no subscription. It is written for budget and older phones, and for shops and homes where the electricity is not always there.

The short answer

Check the battery in three ways before you trust an old phone as a camera that must keep recording through a power cut:

Ask the phone. Some phones have a built-in battery health screen.…