My Macbook Air 2012 - shit just got real

My beloved macbook is now beginning to show its human side, that it's not perfect. Now my battery wont last more than three hours, and kernel_task is taking almost 900 mb with nothing up and running.

I've tried resetting PRAM and SMC, deleting and restarting various apps, and still no change. What to do? And yes, I've checked that I have the lasted flash update.