Dell vostro 15 3500 battery draining

I bought dell vostro 15 3500 on 28 January.....

Within months its battery drains so fast ....I don't know why this is happening 

My laptop battery backup is just between 1:30 hour to 2 hour....

I put my laptop on aeroplane mode ...

Also reduce the screen brightness...

And also decrease the refresh rate for better battery life .....

But this is not working...

Battery drains fastly ...please anyone help me