Battery Backup Time Reducing Rapidly.

I've a New Toshiba laptop. The battery timing was more than 4 hours when I bought it, but for the past few days, the battery back up is reducing rapidly.
It used to consume only 25-30% within the first hour of use, but now it almost consumes half of the battery within an hour.
Please see the image below:

It was fully charged about an hour ago & see it consumed half of it within an hour.
Why my battery life is reducing? Should I claim the warranty?
