What was found
DURING COCKPIT PREFLIGHT INSPECTION, LT PFD, MFD TURNING ON THEN GOING BLANK, FMS LT & RT START DOING THE SAME, RT SIDE PFD ALSO TURNING ON, THEN BLANK. APU RUNNING & GEN OPERATING. APPEARED TO BE CONTINUOUSLY SURGING. MCC SUGGESTED SHUTDOWN REBOOT, ON REBOOT BATTERY VOLTS 21, UNABLE TO START APU. CHECKED FWD SERVICE COMPARTMENT & CHECKED BATTERY BOX FOR HEAT, COULD SMELL BURNING ELEC SMELL. REMOVED MAIN AIRCRAFT BATTERY PN: 405CH10 SN: A03172 AND INSTALLED AN OVERHAULED UNIT PN: 405CH10 SN: T00882. OPS CHECK GOOD IN REFERENCE TO F2000 MM 24-32-01-900-801. NO DEFECTS NOTED AT THIS TIME. VERIFIED ELECTRICAL SMELL COMING FROM MAIN SHIP BATTERY.