There was a question asked on 6/11/20 https://dinonline.org/2020/06/11/recharging-hearing-aid-batteries-on-shabbos/ about choosing hearing aids with regular batteries rather than buying hearing aids with batteries which require recharging.
The answer given was to get the non-rechargeable. One of the explanations was that the batteries and the charger are muktza.
The patient/consumer did not ask the question correctly. The rechargeable batteries are not removed from the hearing aid and placed in the charger. Rather the entire hearing aid is placed on a charging dock and later removed.
Assuming this can be achieved without turning the charger on and off ( such as having the charger on a timer to go on after the hearing aids are docked and off before the hearing aids are removed from the dock) would using rechargeable hearing aids on Shabbos be an option?
If you don’t have to remove the batteries, or recharge it on Shabbos, because it will hold its charge from before Shabbos until after Shabbos, then the rechargeable ones would be the same as regular ones. The issue is placing it on the charger on Shabbos, but if this is not needed then it is fine.