Below is what the PD9200 manual says. Based on this, I would say the Converter is failing to sense voltage on the battery correctly. It's also possible that somehow it has been switched manually to BOOST mode, as it can with the optional Pendant, and is stuck there.
I'd suggest turning off the circuit breaker to the Power Converter (or the 50 amp mains), and turning the battery cutoff to OFF to see if it will reset to normal operation.
One other thought. Turn the battery cutoff OFF and leave it that way for 20 minutes and then take a voltage reading. If the batteries still read 13.6V, then you're back to the Power Converter.
If the Power Converter stays stuck in 14.4V Boost Mode, I would replace it.
The full rated load is available for load, battery charging or both. When functioning as a regulated battery charger the INTELI-POWER 9200 converters have nominal voltage output of 13.6 VDC. The system was designed to sense voltage on the battery and automatically selects one of 4 operating modes (normal, boost, storage and equalization) to provide the correct charge level to the batteries.
CAUTION
IT IS IMPORTANT THAT THE FLUID LEVEL OF ANY CONNECTED BATTERIES BE CHECKED ON
A REGULAR BASIS. ALL BATTERIES WILL “GAS” AND LOSE SOME FLUIDS WHEN
CONTINUOUSLY CONNECTED TO ANY CHARGING SOURCE.
NORMAL MODE: Output voltage set at 13.6 volts DC. This voltage provides good charging rates and low water
usage.
BOOST MODE: If the converter senses that the battery voltage has dropped below a preset level the output voltage is increased to 14.4 volts DC to rapidly recharge the batteries.
STORAGE MODE: When the converter senses that there has been no significant battery usage for approximately 30 hours the output voltage is reduced to 13.2 volts DC for minimal water usage.
EQUALIZATION MODE: When in storage mode the microprocessor automatically increases the output voltage
to 14.4 volts for 15 minutes every 21 hours. This will help to reduce the buildup of sulfation on the battery plates.