For those who try to replace battery for rechargable hearing aids, better do some waterpoof for the batteries

Better waterproof the lithium battery. I think you can use waterproof glue. My battery rusted after I changed it for about a year.
If lucky, only the battery will be rusted, but if not, the rust may spread to the body and the aid dead. The original battery is surrounded by a plastic shell, which is probably for waterproofing.