From the date of manufacture most batteries will store well for up to four years. Check the expiration date on batteries before you buy them, a date two years out means that those batteries have been sitting on a shelf somewhere for two years already.

Batteries come in four standard sizes that are numbered and color coded. Size 10 batteries are coded yellow, size 312 are coded brown, size 13 are coded orange, and size 675 are coded blue. Quite often manufacturers add a letter after the number such as 13E or 13A. These letters only signify the manufacturer and have nothing to do with whether the battery will fit your hearing aids.