Here is what I did to replace dead batteries in my Phonak Audeo M-50.
I would first suggest to read this thread: Insight into the inside of the hearing aid. It contains a lot of usefull infos and photos
Strategy used: remove te dead battery from its plastic casing, slide a new one in place and
reconnect the 2 wires to the main circuit
Parts used:
1- Battery from this supplier:
https://www.alibaba.com/product-detail/M7854S1-ICR7854-LIR7854-3-7V-25mAh_1600227890083.html
2- Electrically conductive glue/paint. It is more paint than glue (low viscosity) but it works
https://www.amazon.ca/Conductive-Electrically-Adhesives-Conduction-Connectors/dp/B09KVK5NB3?psc=1
Steps for the battery replacement:
1- Remove the receiver
2-Open the external enveloppe and remove the first half
3- Remove the second half
4- Using the heated metal tube, remove the flat battery casing sides. To disconnect the wires from the battery, I used a thin knife inserted between the wire and the battery.
5- Remove the battery from its casing noting its polarity
6- Insert the new battery in the casing with the correct polarity in the right place. It is critical. Be sure that the end of the wire is bare (no isolation)
7- Glue the first wire on the new battery and let the glue dry for a couple of hours. Repeat for the second side.
8- Place the HA in an owen at temp. 50-55 deg C for 24 hours. Note the glue will be conductive only when completely dry
9- Re-assemble and place in the charger until the green light stays on. Be sure that the charging contacts protrude enough for charging
Results:
Both HA work now as new.
When used for 15 hours in a quiet surrounding and connected to phone (left side) but no streaming, I get the following battery level:
Left 60% Right: 70%
So, repairing the first one is somewhat stressing but once the process is established it will be a lot easyer for the second one.
The device and parts are very tiny. Work slowly and take a lot of reminder photos.
Note the piece of wood and the rubber band that I used to hold the device when necessary.
Feel free to ask questions.
I hope many will successfully do it! Let me know…
Happy new year!
See the photos below