Contactless Charging Of Hearing Aids

Conventional hearing aids need batteries of size 13 (7.8 mm in diameter and 5.35 mm in height). By replacing the battery with one of a smaller size, a volume of 7.8 mm in diameter and 1.9 mm in height was gained to integrate a secondary coil and charging electronics.

Different coil types and positions were investigated to minimize eddy current in the battery and maximize the efficiency of the electromagnetic transmission. To ensure safe battery charging and discharging, the whole electronics is integrated into the given space and controlled by a tiny microcontroller. As the battery is based on a new chemistry (silver-zinc based), different charging algorithms were implemented and evaluated.

Project Targets

Most hearing aids are powered by non-rechargeable batteries.To improve ergonomics and usability of hearing aids, an inductively chargeable retro-fit battery module for common hearing aids was developed.


Very small physical size of PCB and secondary coil

Battery must supply the hearing aid for at least 18h and be charged again within 6h

Intelligent charging control with battery voltage and charge current monitoring


During this project, an inductively chargeable retrofit battery for hearing aids was developed, integrated and tested. This retrofit module includes a silver-zinc based battery, that can be charged inductively and may replace a conventional battery of size 13.

Project Partners


Project Duration

2011 - 2012
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