Okay, I think that makes sense now. So basically (from the perspective of the pilot), powering the instrument panel and center console can be done with the BAT/DCT switch, but to start and do anything else the BAT EPU switch must also be engaged. If the EPU is actually plugged in then you will get the GENE and BATT warning light until it is unplugged. Out of curiosity (not that anyone would do this) does anything happen if you turn off the BAT/DCT switch in flight?