As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING TS OF A STBY INST BATT FAULT CYAN CONDITION, IT WAS NOTED THAT THE R ESS BUS AT THE RT CB PANEL WAS ONLY READING 24.5 VDC WHILE THE RT MAIN BUS WAS READING 27.5 VDC. THIS WAS WITH A GROUND EXTERNAL PWR CART PROVIDING PWR TO ACFT. PWR CART OUTPUT WAS SHOWING 27.9 VDC. TS ONGOING.