While en route the flightcrew received an AIR/GRD SYS message, an illumination of the standby power bus OFF light, and several advisory and status messages on the engine indicating and crew alert system (EICAS). ... QRH ... AIR/GND SYS message. The flight crew then followed the procedure referenced in the QRH for STANDBY BUS OFF by turning the standby power selector to the BAT position. The QRH procedure also referenced that, "The battery will provide bus power for approximately 30 minutes." The airplane systems stabilized with several items inoperative and the captain contacted maintenance technical support and subsequently elected to continue the flight on battery power
Approximately 1 hour and 40 minutes later, while in cruise flight, the battery power was depleted at which time several cockpit electrical systems began to fail. ... over western Michigan and the captain elected ... divert to ORD.
It appears that, other than the BAT SB discharge light, there were no other abnormal electrical indications. Once all 4 busses failed, they realized they had a total different set of problems than what the QRH led them to believe. They didn't want to go around to a longer runway with the flight control difficulties. All told, an excellent outcome. Well done guys.
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What depth of systems knowledge and logic would lead to this sort of conclusion?