I have my 645 (no music) for a good year now iirc and never had any problems with the battery. But since yesterday, I have massive battery draining issues. I charged it 2 days ago in the evening and notices yesterday morning, that it was low again. So I charged it before going on a run. Didn't think more of it but then in the afternoon it was low again. Charged it again before going to bed but it didn't even last the night.
I just recharged it now and it already lost 5% while I wrote this post.
Any idea what could cause this? I rebooted it multiple times already and it hasn't fixed it.