Battery Problem ?

[gp123]

After 6 months of predictable battery performance my N7 (2013) suddenly requires more frequent charging. I see that apps at start-up are as expected; app power usage seems normal;  Wifi, gps, bluetooth are off when nor required, and usage are as they always have been.   Battery discharge is noticeably faster than before.

Also, full  start-up (from power-off) seems slower.

Perhaps there is something running in the background that I cannot see, or there is wake-lock activity. Is there a tool or procedure that can determine this? (My Nexus in NOT rooted).  Perhaps the battery itself has degraded over time

Any suggestions on how to track this down?