weird battery percentage topic

I've recently flashed v20h kdz with lg flash tool 2014 and the problems began. When i plug in the charger the battery level stays the same, I have to reboot the phone to display the correct percentage. While using it, the percentage doesn't modify untill I turn the screen off and let it for a time.I 've downgraded to 4.2.2 and it keeps happening. Solutions?My phone is 1 month old.