HTC ONE M8 running Kitkat (4.4.4). Latest version 10.2.98 (038) has been much more stable and gentle on battery. All versions after 9.0.82 (038) had bug - Play service continously keeps device awake (even when no apps running  WiFi off  data off  Bluetooth off  GPS off  Auto Sync off and screen off). Latest version 10.2.98 (038) has the same problem but is better/improved than other recent versions. There are still unnecessary wakelocks causing battery drain. The issue completely resolved when I downgraded back to 9.0.82 version - so this is clearly NOT a hardware/battery problem.
April 28 2017