I have over the years replaced many batteries not intended to be user-serviceable (because they wanted to coerce a new wasteful purchase). I've done it to razors, I've done it to electric toothbrushes, I've done it to several smartphones.
The smartphones required the most effort, but it's feasible for anyone able to make it. Resources like iFixIt.com will help with repair guides for specific phones.
Don't give in!