Default [Q] Sudden Battery Drop

I am using Micromanax Canvas HD from last 8 months with custom ROM Stark HD. After using that much months i am facing a weired problem my dropped after 50% to 30% very fast then 30% to 15% very very fast. Some time i have fully charged my battery and when i removed the charger its shows low battery. I correct this problem after removing the battery and reinsert it.

Please tell me any solution of this.