My early 2015 macbook pro battery has had the "service battery" warning for over a year now. I hit the 900 cycle mark before last summer, and now I'm at about 1000. The battery lasts for < 1 hour, but I rarely use it without plugging it in to the power nowadays. I'm going to get the battery changed sometime in the next couple of months -- it's difficult for me to be without my mac for an extended period of time at the moment.
With that said, I've noticed that my macbook performance isn't as great as before. It seems slower and hotter even though I'm using it while plugged in to the power outlet. Does a deteriorated battery affect performance of the mac when it is plugged in to a power supply?