Are you referring to “custom hearing aid molds” for the Naida Marvel? Not sure but in any case I’m doing a little homework and it appears the Naida (M) will accept size 13 disposal battery. Not sure about rechargeable. Also in the link below I’m seeing a “classic ear mold” or skeleton mold which tells me the receiver must be inside the the HA case.
I’m also assuming the zinc-air battery (size 13) that’s recommended is not Zpower brand that’s gotten negative reviews.
Lastly regarding Phonak’s notorious pairing issues with bluetooth, it appears the Naida M is like previous marvel brands in that you have to turn aid off and on to connect to each individual bluetooth connection. Per link - It is only necessary to perform the pairing procedure once with each device featuring Bluetooth wireless technology. After the initial pairing, your hearing aids will connect automatically to the device. This can take up to 2 minutes.
Since the Phonak Marvel has now been out 18 months plus I would of thought the compay would of addressd the bluetooth parring issue, especially in 2020 hearing aids such as the Naida M. I’ve now concluded that this parring issue will probably never be updated beyond its current capabilities.