My Advent 5431 laptop is dual booting windows 7 and ubuntu and has a U40-3S3700-B1Y1 battery pack. It says that it is always charging even when the charger is unplugged. Why would this be? When I unplug the power cord it continues to say that it is plugged in and charging but the battery life goes down until it powers off without a warning.
Your battery may be broken and supplies power with a higher voltage than what it is designed for. I would suggest you measure your battery and see if it delivers the correct voltage. The other (more likely) scenario is that you got some fried electronics in your laptop that incorrectly indicates charging (if the same behavior is observed in both Windows and Ubuntu).
If it is for both OS the same (your comment at the question) I would check firmware.
This means: Is there a new BIOS for your Laptop available? Install it. Maybe that already fixes your problem.