Macbook Pro is running very slow

I had my OS updated to Yosemite. However, after a few days, my macbook started running very very slow. I had it checked at a nearby iStore and they diagnosed it with some sensor defect. They advised to change the logic board of my computer. On the other hand, they found an alternative solution to my problem. By removing the battery, my laptop runs its usual speed.

I didn't have my logic board replaced because I'm not sure if the problem is really there. I don't understand why my macbook runs its usual speed after the battery is removed. Can anyone help me understand what's happening with my laptop? Is there a way to fix this without changing my logic board or removing its battery?