Q: Kernel Task 360% when MagSafe is disconnected (Early 2011 Macbook Pro) please Help!

I have an early 2011 macbook pro, 2.3 GHZ Intel Core i5, 8 GB RAM, and a 250 GB SSD (Intel HD Graphics 3000)

- When I plug it into the MagSafe it works perfectly, no issues or problems.

- When I disconnect my Macbook pro it shows kernel_task to be 360%+.

     - I can barely move the mouse, it can barely do any tasks.

     - I've been stuck with this problem for the past 3 years, and I replaced the HDD with and SSD , and ram from 4GB to 8GB about 5 months ago.    

- Sometimes my macbook says replace battery, other times it says my battery status is normal. I don't know what to do, and whether it is a problem with the battery (since it is 5.3 years old).

- I tried the method for deleting a p.list that was in a kext file showing Macbook Pro, 8,1. This method worked, but after a while boot times were affected tremendously, so I Clean Installed my OS X, as I was worried that this would put a strain on my Newly bought SSD.

- Please Help me, I've been stuck with this problem for almost 3 years +.