That model of Dell laptop battery has been known to go bad. I set it aside and put in another. (I have lots of them.) After a few minutes, it also turned red and I pulled it. Same for the third battery. Fortunately, the fifth battery worked, as did the sixth, and there are others available if I need them.
I also managed to (eventually) get the legacy job done. Although Dell might possibly still replace the old defective batteries, I'm not sure there's much point, given how rarely I use the old Dell machines. I may just take the defective batteries with me and put them in the battery-recycle box at work. But I'm sure glad I was paying attention, because I really don't want a battery fire, and that first overcharging battery felt almost hot enough to burn my hand when I pulled it out.