Hey, please update to the latest version of Flyme with clear data ticked and drain the battery of your phone completely. After that, charge the phone continuously while switched off from 0 to 100 and leave it for 2-3 hours at 100% charging. This will recalibrate your battery and the phone won't lose charge this soon.

you can follow,my battery saving tips
http://forum.flymeos.com/thread-31274-1-1.html

Please use latest Flyme update