1. Check which way it faces
Most coin batteries go in with the + side, the flat side with the writing, facing up or towards you. A battery put in upside down does nothing.
2. Peel off any sticker
Some new batteries come with a clear film or a sticker on one side. Remove it, or the battery won’t touch the contacts.
3. Look for a bitter coating
A few devices, like the AirTag, can’t reach through the bitter coating on some coin batteries. Try an uncoated one.
4. Clean the contacts
Wipe the metal contacts with a dry cloth. If a spring contact is pressed flat, bend it up very gently so it touches the battery.
5. Check the exact code
A CR2025 fits where a CR2032 goes but is thinner, so it may not touch both contacts. Buy the code printed on the old battery.
6. It may need to reconnect
Some car keys, sensors and trackers need pairing again after a battery change. Your manual or app shows how.