Mac is slow when not plugged in
I was having major issues with my mac. It was incredibly slow and some programs would cause the mac to freeze. I reinstalled the whole system a number of times. I now have a macbook pro that is exactly like when I bought it. I deleted almost everything off it. It runs great, when it is plugged into the charger. The battery is fully charged. The laptop will run without the charger just exceptionally slow. In addition to this, I still have the problem of some programs causing the laptop to freeze - for example chrome.
Has anyone got any idea what is wrong with this please and is it fixable by myself ? Im getting a new macbook for work reasons, so i'd like to refurbish this to sell/give to someone.