i experienced the same issue, but i found out it is because i never power cycled..... meaning i never let my phone die and would always charge it before it died.. so here is what i did ro fix that issue
1. use your phone till it dies
2. let it charge untill its back at 100% ( green light )( An charge it with the phone off )
3. once fully charged boot your device and repeat steps 1-2 again and it will fx the battery issue
I don't know much about the android so I can only tell you the phenomenons that I observed. Maybe my words are hard to understand. Sorry about that, I'm Chinese.