The company ZPower has recently released a rechargeable 312 and 13 battery based on Silver-Zinc technology. These batteries deliver a higher voltage than standard Zinc-Air cells and must only be used for hearing aids specifically designed for them. Other hearing aids can be damaged by this higher voltage. These special batteries can be identified by a green border.
Phonak hearing aids are designed for disposable Zinc-Air (not Silver-Zinc) batteries which provide 1.4 Volts.