Older MacBook models, especially the ones made before 2008, have this strange problem where they suddenly slow down when you remove the batteries and just work on wall power. Many people have been very confused about this problem, wondering why is my mac so suddenly slow when they have gone to wall power, which ideally should allow for more stable performance. After all, it makes sense that way. When on batteries, you expect your Mac to have unstable performance as battery power is constantly coming down. Wall power is super-stable. Then why does this happen?
It is because of an inbuilt feature called Speed Step that is built into older MacBook models. Older MacBook models are designed in such a way that they treat wall charging power and battery power separately.
What happens here even if you are using wall power is that your Mac looks for battery power as an extra source of power when your CPU is running at very high levels. So, when you don’t have batteries to assist during this request for more power, your Mac plays it safe by throttling back the performance of your Mac, by slowing everything down. You will most probably see a beach ball loading screen when this happens. Apple in their owner’s manual have strongly recommended that Mac users do not use their MacBook without batteries. If you have removed your batteries because they are too old and do not charge properly, it probably means that you have gone over the charge cycle limit for those batteries, meaning that you have to swap them out for new ones. Yes, it is an expense, especially at the rates at which Apple’s sells its accessories for. But then, there is no point trying to save about $40 when you are putting a much more expensive MacBook at risk of malfunctioning.