My 2004 Prius (55K miles) recently developed a problem the dealer can't diagnose. Gas mileage (highway) has dropped off 15% and when the battery meter indicates two bars, it lags when accelerating from a stop. I've noticed that once the engine is warmed up and I park the car but leave it on, the meter runs down from six or seven bars to two bars in less than five minutes! I checked a friend's Prius and the meter didn't drop at all while I waited seven minutes. There are other abnormal indications but anyone out there notice the time it takes to discharge while parked?