I'd suggest you call Dell tech support on this one. Either the battery is dying and the computer is indicating it has more capacity then it really does or some re-calibration effort needs to be taken that Dell might be able to direct you on. A lot of Dell batteries have a test button on them with a series of lights that indicate the charge state. I would suggest if present, you push that when the shut down occurs. If the lights are all out or only one LED lights, then your battery is not as healthy as you would think. In any event chasing other hardware possibilities seems pointless unless you know the battery is healthy. Everything is fine when plugged in... right? In my opinion the only thing going on here is a disconnect between what the computer thinks the battery charge state is and what the actual charge state is. No big worries.