Why is my battery draining so fast????

[AC Question]

..Before, i'm using my phone(watching youtube videos and playing asphalt) while charging and the percentage still increases..but now the percentage stays still and even decreases..

 

[B. Diddy]

Welcome to Android Central! Which phone? Are you charging from a wall outlet or computer USB port? Has there been any change in the mobile signal (i.e., is it weaker)?