[Q] LG Optimus L7 II (P710) - Battery Problem topic

Hello guys! I have problem with battery in this phone, battery is drain too fast when I install offical update for KitKat (4.4.2). In CPU-Z my battery is 1500mAh but battery is 2460mAh. Where is problem? How to I downgrade to old android jelly bean without rooting? Sorry for my bad english. Thanks!