There are two types of battery tester – digital battery tester and keychain battery tester. Digital battery tester is easy to use, lightweight, compact and portable device that quickly determines if your hearing aid battery is good. It tests all sizes of hearing aid batteries on a digital display. Keychain battery tester can be placed on your keychain, so that you are able to test your batteries at any time. Its built-in battery holder (up to 2 pieces) also makes it easy to store extra batteries.