Superstition: it used to be the case that leaving a device on a charger was hard on the battery. I think that has been fixed by smarter charging circuitry. But I don’t really know any of this because manufacturers don’t want to tell customers this kind of thing.
Perhaps you have a background task that is using a lot of CPU and thus causing the system to burn up more battery. I’m not an expert Windows user, but I think “Task Manager” might show you where you what’s up. I’m sure that there must be better tools.
https://superuser.com/questions/398342/windows-notebook-power-consumption-monitor
.
