Hi
Try this:
Disconnect AC
Shutdown
Remove battery
Connect AC
Startup
Open Device Manager
Click the plus (+) sign next to Batteries category, right-click All of the "Microsoft ACPI Compliant Control Method Battery" listings, and select Uninstall In the "Confirm Device Uninstall" dialog box, click OK. (it’s ok if you only have 1 of these listings).
Click the plus (+) sign next to System Devices.
Right-click the “ACPI Fixed Features Button" and select Uninstall. In the "Confirm Device Uninstall" dialog box, click OK.
Shutdown
Disconnect AC
Insert battery
Connect AC
Startup