Haven't tired that one, but It my be too late...I think I'm going to need a New Battery.
It's not new, but I think over time..I have been draining the Battery by keeping it in..Or maybe what you said.
My battery always stays in when using electricity, has no effect on the battery.
My Dell is 3 years old, can run 4 hours without electricity, however todays models can go 8 + hours.