Kernel task 100% cpu

Performance of my MacBook pro dropped drastically since last boot, to the level even mouse movement is not smooth anymore. The system was in sleep mode and drained the battery completely. Upon restart it was sluggish and battery does not recharge (MagSafe indicator remaining green). The process kernel task takes between 500 and 700% cpu and 750mb ram, making the machine useless. No programs active apart from activity monitor, no external hardware attached. The system does not heat up, fans are not spinning.

After reading some blogs i tried several things, without any result. In safe mode cpu usage remains low, but the system remains slow as well. Normal reboot brings back the problem. Resetting SMC and PRAM does not solve the issue.

Any idea what could be causing this and how to fix?

MacBook pro late 2011, 8Gb ram, 1Tb SSD, osx Capitan