SolvedVRDP18700 | Hearing aids and induction loop systems: batteries for cochlear implants
From HM Revenue & Customs · VAT Relief for Disabled People Manual
The batteries for the implant are eligible for VAT relief as an accessory to an aid for a disabled person provided that the batteries are designed solely for use in the appliance under item 2(h) (see VRDP05100).
Standard, general use batteries do not qualify for relief even if purchased for use in the implant.