An old battery can load down the charging circuit and create other issues. It's time to decide if you get a good new battery or run without.
As to why, there are so many prior discussions that I defer to those ideas. Here I'm more concerned that leaving an old battery in could result in a motherboard failure.
I have a Dell XPS m1730 and i use it for gaming. (Not big intense games)
Lately i have realized that my battery is trash, which is understandable for a 11 year old laptop. But ive noticed if i start up the laptop without the battery my fps goes up significantly. If i start it with my battery in it, it is slower. Just recentally i tested something and removed the battery, started it up, turned it off, put my battery back in and started it up again it was still at a high fps.
(my laptop is always plugged in and remains on my desk 24/7 although i turn it off at night time)
Does anyone know why my battery makes my laptop slower in some cases?