1. The colours are the quickest clue
Yellow is size 10, brown is 312, orange is 13 and blue is 675. If you keep your spares in a tin, sort them by colour and you’ll never guess wrong.
2. Size 10
The smallest, at 5.8 mm across and 3.6 mm thick. It goes in in-the-canal and slim receiver-in-canal aids, and it runs out fastest, usually after a few days.
3. Size 312
7.9 mm across and 3.6 mm thick. This is the most common size, used by most behind-the-ear and receiver-in-canal aids. It usually lasts several days.
4. Sizes 13 and 675
Size 13 is 7.9 mm across and 5.4 mm thick, and size 675 is 11.6 mm across and 5.4 mm thick. They’re the big ones, for power behind-the-ear aids, and they last the longest, often over a week.
5. Check the old battery
The size is printed on the flat back of the battery and on the packaging. Match it to your aid, and keep each size in its own labelled container.
6. Sizes aren’t interchangeable
A size 312 is wider than a size 10. It won’t fit a size 10 aid, and forcing it can damage the door and the contacts.