[ptero]

I think replaceable batteries do not present big problems for water resistance. Water proofing is another story, but at least IME water resistance to a decent level is enough.

For example, I have an old GPS+HRM runner watch which is water resistant but not fully water proof. After a run I briefly wash it under running water (not submerging, but heavily splashing and using soap). I have been subjecting this watch to such abuse for years and it has not failed yet.

I think for most users water resistance would be just fine, although this may be just a personal bias.