Handy Rayovac battery tester. Suitable for all sizes/types of zinc-air hearing aid batteries, 1.4v. The Rayovac battery tester has a digital display and has been designed in the form of a key chain. The Rayovac battery tested also has a small storage compartment/drawer where two (spare) batteries can be kept. The Rayovac battery tester is easy to use. Simply lay the battery on the front surface and push the bracket to make contact. This little device shows how if the battery has any charge remaining. Please note: NOT suitable for rechargable batteries.