I had the same problem (to my understanding) on a Huawei device. What helped me was to really drain the battery, then make a full charge, and then drain it completely again. What this supposedly does is re-calibrating the battery level, which was way off for me.

So, try to run the mobile as usual (I'd remove root, but that shouldn't be necessary) and when it dies, do NOT charge it. Instead power it on again and let it run as long as it can. Repeat an infinite number of times, or until you feel you're turning crazy, and THEN charge it full. Repeat the draining process, and then give it one more full charge and see if the battery level now is correct again.

Just remember to set the mobile on silent mode before you need to restart it over and over. ;-)