I'm noticing that when I start using my SP2 with its Power Cover (both @ 100% charge), that the Power Cover's battery level starts dropping like a rock for whatever reason. Within a couple of hours of just web surfacing or other un-demanding use, its level goes down to 50% or lower. I'm wondering if the metering of these levels (BatteryBar Pro), reads somewhat disproportionately? Overall, I'm probably getting about 9-12 hours of use from both. Is anyone else noticing this issue?