Weird Battery Percentage on iPhone 6s When Charging

My 3 weeks old iPhone 6s 64gb had an annoying issue when charging.

My iPhone 6s battery percentage will getting stuck if i put charging on airplane mode with screen off/sleep.

For example when my battery on 41% i plug in for charge and enabling the airplane mode and then we know that the screen will going to sleep itself (based on my autolock settings set to 1 minutes), after that for the next 15 minutes the battery percentage will only always showing stuck on 41% !!

BUT when i put the screen always on/unlock, the battery percentage suddenly will updates so very fast! Weird.

I do calibrate the battery, restart, force restart, reset to factory settings, clean restore (not restore from bakcup), this issue still exist.. I also use the original charger adapter+lightning cable.

i have this issue since ios 9, 9.1 and 9.2, those recent update does not solve this battery percentage stuck issues on iphone 6s.

Dose anyone had a same issues ?

Please apple, this is very annoying.