Dual batteries; reads both but only uses one.

My Laptop/tablet has a primary battery and a secondary media bay battery. Both can be seen in the power mangement icon, as well as their charge state. The problem is that once the secondary battery is drained the system goes immediate shutdown rather than using the primary battery.

If I remove the secondary battery, and unplug the AC power, even if the primary battery shows 100%, my laptop can't boot/run.

Details:
- Windows 7 Professional 64-bit
- Laptop is less than 5 months old, including both batteries.
- Both batteries worked fine 1 week ago.
- Everything is OEM
- Fujitsu Lifebook T-Series (T902)

Any help would be much appreciated. Thank you.

PS: Also, if this is in the wrong place, please let me know.