I am not sure if this is correct, this is what I did (from memory) last week when bat dead.
turn on generator
turn engine key to right, on position
push in white rocker switch
turn on gen
turn on key
go away/wait 5 0r ten min
I don't remember if manual told me about this or if Amanda did on the walk through
I hadn't thought about turning the key on; there are two ways to close the isolation relay between the house batteries and the engine battery, one is to press and hold the white momentary rocker switch and the other is to have the key in the "run" position. That is how the engine alternator charges the house batteries when the engine is running, the relay is closed all the time the engine is running and opens when off so that the engine battery is isolated and won't be discharged.
Since it takes a few minutes to charge a dead engine battery through the relay, turning the key to "run" may be easier than holding the white switch. There may be some concern about all the engine electronics being on while the key is on but the engine is not running?
So, Kevin's procedure worked because the key was on, pressing the white switch did nothing if not held on. Also, running the generator while not necessary, may charge the engine battery quicker since the house battery charger is operating and charging all the batteries instead of just equalizing the charge from the house to engine battery.
So, the bottom line is you have to hold the white rocker switch on, or turn the key to "run", or as Keelhauler did, replace the momentary rocker switch with an on/off switch.