Originally Posted by Tfryman
Well that's the second part of the mystery.
1. Why wasn't it kept charged regardless of the USE/STORE switch position?
2. What could be draining it?
Your dash radio does have a constant 12 VDC line to maintain memory settings that goes to the chassis battery. I'm not sure what other constant 12 VDC load would come off the chassis battery.
The entire front cap is powered by the chassis battery through the 100 amp circuit breaker under the hood by the chassis battery. The fuse panel down by the drivers left foot distributes that electricity. Things like mirror heat,mirror controls, fans, map lights, windshield wipers power to the jacks controller, ect. all come of the chassis battery. The only exceptions are the Ford supplied items, the chassis A/C, the radio and the 12 volt receptacles which are supplied by the Ford power distribution center..