HMm; I don't know any "discounter sellers" Phonak or other? Careful because most of the newer/rechargeable hearing aids are disposable after the rechargeable batteries get depleted after a few years. Suggested DIY School Hearing Aids (v2.0) reading are PDF files named (Li-ion Rechargeable Battery History) and (Li-ion Rechargeable Battery Replacement).
Also; the DIY School Hearing Aids (v2.2) access portals are at your finger tips via 24/7 cloud storage access.