VAIO Pro battery level not updating while using

Recently, a strange thing happens to my Sony VAIO Pro 13. When I use the laptop on battery, the battery level just won't change at all as if it's on AC adapter. Always 100%. Then suddenly, the battery level will drop to a certain level after 3-4 hours, then after 3-4 hours it updates again. Then without battery level low warning, the Ultrabook close itself. What is going on? BTW, I am running on Windows 8 x64

I've contacted Sony Support staff, and with his indication - something wrong with the service, I look into the services that got disabled, and I did found one - Vaio Power Management Service, after making this service running automatically, things went back to normal. I still don't know how the hell it got disabled though. I didn't fiddle with it.