To fix battery on an MTK device not charging above a certain percentage.
1. Remove the battery and hold down the power button for 45 seconds.
2. Slot in the battery then flash Clockworkmod recovery to the device. Learn how to do this HERE or HERE or HERE.
3. Boot the phone into recovery mode using device specific physical button Combo.
4. In recovery mode, Select Advanced.
5. Select Wipe battery stats.
6. Reboot the phone. DONE!!