I am using those new fangled usb c charge batteries , the actual batterys have a usb port , they are 1.5v , unlike most normal rechargables that are 1,2v , they seem to last longer han normal rechargables

link to some on ebay , all sizes are available https://www.ebay.co.uk/itm/335076828519?_skw=335076828519&itmmeta=01KWNXW09B1HSQFG1Z6HC5KNFY&hash=item4e0422a567:g:g~0AAOSwKkdlL7rq&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xCd26489vRhwhTPSu8IwT8pAeI%2BV7qYY6ayplyr58PzFJKQaJ29wwc3P0bRV5A7XF7wjeWjXelPtxa1ipbb4%2FLXo1AOJyF6DunYAtRHvniUR3pGrN8%2BHyn6PMBsatshUN0QwMoFLRu8EVSs4euWdjdvfxJd8syiXYzZSwAKZ7wITm0gQqP0c8u4GRE5E60norJczVJrFtLFEPkMlCy6PuVgeTo4JF0m2GHTNFm1yKdOjDuY%2BsVt8i6DdE3RDo%2FD0FBIGioAVToS9PzGaJOwg%2Fr%2BsM6e7Iev%2FQU%2Fah6BlMOXxQ%3D%3D%7Ctkp%3ABk9SR-KE8L3lZw