I recently replaced the battery in my Pebble Time Round. Replacements are on iFixIt. It's not easy, but not impossible either. For me, it's well worth another 5+ years of use while I wait for someone, anyone, to make a decent competitor.
I re-sealed mine with Sugru. It is as waterproof as it was before, as far as I can tell. Unfortunately I used too much and some of it got squashed under the glass so it's slightly visible. It's really hard to use the correct (very small) amount. There are other adhesive options that I haven't tried.
