There are four main sizes of batteries, each with a specific color-coded package: size 10 (yellow), size 13 (orange), size 312 (brown), and size 675 (blue). The battery size you need is typically based on the size and style of your hearing aid. Standard hearing aid batteries are zinc-air, which are activated when exposed to air, so it is very important to keep them sealed in their packages prior to use. Never open packages to move batteries to a single container; keep the packages sealed until the batteries must be used in the hearing aids, or you may end up with a dead battery. Don’t buy batteries if the seal is broken.