Beoplay portal battery fully died, what now?

I've had my headset for a bit less than a year I think and I've been having battery issues for a couple weeks. Didn't seem to want to charge fully, light would never turn green no matter how long I left it to charge, and only lasted about 5 or so hours max before I started getting low battery warnings. Last night it fully died and when I woke up the charging light wasn't even on and I can't turn on my headset anymore.

Are there any replacement parts/guides on replacing the battery? I can't find ANYTHING on it no matter how hard I look.