1. Coin batteries
Flat and wide, like a coin. Usually 3 volts and start with CR. Used in car keys, AirTags and computers.
2. Button batteries
Smaller and thicker, 1.5 volts, start with LR or AG. Cheap and fine for toys, thermometers and laser pointers.
3. Watch batteries
Look like buttons but are silver oxide (SR or 3-digit numbers like 377). Steadier power, so watches keep good time.
4. Hearing aid batteries
Tiny, with a coloured sticker. They need air to work, so only peel the sticker when you’re ready.