hello_chandran, You may want to check the 1st and 2nd link below for concerns on battery draining before changing the battery. 3rd link, below is a disassembly video link that will show how to get inside Yota to enable changing of the battery. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.

http://howtodothing.net/yotaphone-2-batt...

http://www.gearbest.com/blog/how-to/easy...

https://www.youtube.com/watch?v=_Kr1dnav...