Widex hearing aid battery size 13. The Widex Batteries for Hearing Aids are coded with colour for size identification and are zinc air batteries. The Widex batteries should remain sealed until you are ready to use them. Open your hearing aid battery door when you aren’t using it to assure that your device isn’t using power when it’s not in your ear. These Widex batteries are also compatible with other leading brands of hearing aids like Siemens, Unitron, Starkey, Phonak, Hansaton, Oticon, ReSound, Bernafor etc..