Even non-removable batteries can be replace. It’s not a self service item.
Yeah, I know they can be replaced. There are even battery kits with tools available, but they are tricky to use. They usually require heat to soften the sealing glue, and then, if you don’t re-seal it correctly, the phone is no longer water resistant.
My current phone is a Kyocera E4810, a rugged, part-smart flip model that isn’t junk like the cheap flip phones, and isn’t as surveillance friendly as the usual smart-phone. Also, in spite of the fact that both its battery and 64 GB microSDXC (which I added) are easily replaceable, it stays water resistant. I think it has been discontinued (of course).