I find that if I leave my SP2/Power Cover "charging" for a couple of days or so, even though it's charger light has gone out, the SP2 itself may show a 100% charge, the Power Cover sometimes shows practically no charge, or just a very few percent? I make it a point to open Task Manager just before putting the SP2 to sleep to insure that there's no programs open whatsoever. For whatever reason, it seems to charge up fully (100%/100%), but then, for whatever reason, use up the majority of the Power Cover's charge while just sitting there. At other times, I'll find both batteries at full charge after a day or two left on charge. What the Heck is going on here anyway?