Odd, only time I see a battery do that is when the battery is shot and the cells are not holding a charge.
But at the same time, just last night while I was working my Windows 8.1 machine (I hate Windows 8, cant wait for 10) and then all of a sudden vmware just crashed and wouldnt open, said internal error. I have a ups and have the usb from the ups plugged into the system so I can see when I go to battery for any reason. I look down at my battery icon and it says plugged in, not charging. Just happened out of no where.
So I rebooted Windows and vmware started working again and the battery icon was working again. Just really odd how it would just flip out while I am in the middle of writing code.
So I say for you, to find out if it is the battery or windows is to take Windows out of the mix for a test. Download Ubuntu and you can run it right off the cd or usb without installing it. Then you can see how the battery reports there. If the battery shows the same problem then you know it is the battery. If the battery shows fine and proper then you know it is Windows
Shane