Low battery life in Windows 7
From a discussion in the Microsoft Technet site it appears that Windows 7 has an issue with battery management. A few other sites have picked up on this issue in which Windows 7 will warn about exhausted battery prematurely and recommend replacing the battery.
We have found this issue on an HP NC4200 and a Dell D420. While we do not think actual battery replacement is needed, we do recommend opening a case with the vendor to pressure Microsoft to resolve this issue quickly.