Let me approach this from a different angle with a few questions:
First, you noted that even plugged in you seem to be slowly losing charge. So...
1) Are you using the original charger that came with the laptop?
2) If you power OFF the laptop for a while (I would give it a good 30 minutes at least) making sure to note the percentage charged before doing so, and then power it back on, does Windows indicate that the charge level has increased during that time?
3) Is there a physical light on the laptop that indicates when the battery is being charged and is it illuminated?
What I am getting at:
If you are not using the original AC adapter, it's possible that you are using an adapter that cannot provide sufficient power. A typical symptom is that it will power the laptop to some degree, but you can potentially lose charge, possibly slower than when running purely on battery, especially when doing anything more power hungry. If the laptop is charging when powered off, that is another typical symptom of this issue as the laptop will gain charge because the laptop is not drawing any power.
