I was at a friends house today and he was working on a 99 Cirrus. He said it was going down the road, all the sudden stalled and on the dash flashed "CHECK BUS"....and then it wouldnt start back up..

When he hooked a charger to it, the ammeter readout on the charger was bouincing back and forth.... When you turned the key the dash cycled (RPM bounced to 5500 and stopped)

Any ideas on this? Where to start? Thanks