Samsung S3 neo battery life started to reduce rapidly from 2 days

I am using a galaxy s3 neo phone from almost 8 months, from two days I was using my computer internet in my mobile through usb. Then yesterday night while sleeping the battery was 47 percentage , and morning when I got up and used my phone it got off because of low battery. I dint face this problem from past 8 months, but from two days the battery is reducing a lot even if I am using or not using. Please can anyone say what measures should I take to make my battery as normal???

Thank you in advance