Okay, This may be a big clue that we have missed!
some have other thoughts but many owners manuals state that it is a good idea to have the engine running when we are trying to use the power hungry items like jacks and slides.
One of the easy ways to help any large motor run best is to give it full power.
When we have the engine running Winnebago that I know about will all have some system to tie the coach and chassis battery systems together. This is one way that they give us to do "some" recharge on the coach batteries as we drive to the next site.
Since the normal engine alternator is often really much bigger than any load we put on it, why not let it add a bit of power back to any rundown battery?
One of the quicker ways to avoid giving questionable power to jacks or slides is to simply have the engine running.
For the question of which battery is used? I think that will vary but I can't actually look as the jacks are considered an added part to the RV and not well addressed in the drawings.
But when wondering, one way to decide which battery is used is to watch which battery has the big voltage drop when the ignition is off. Where you were looking at the voltage that dropped from 12 to 10 will be the one the jacks were using.
But that is where we can avoid the question by starting the engine first. With the engine running we get the chassis battery, the coach battery, as well as the engine alternator ALL helping as they are all tied together at that time.
Looking at drawings here:
I see I failed to mention starting the engine before trying to start the generator but that is also a good idea as the main engine is normally much quicker starting than the generator.
But this is the setup on the '04 sightseers. There is a solenoid often called mode solenoid which has control leads from the aux or boost switch near the driver as well as a lead from an ignition point called igntion hot by some builders. Later models that use solid state call it a battery isolation monitor (BIM)
When power flows down lead LR and through the solenoid coil to ground on
lead FM, it operates the solenoid to close the contacts between the coach I marked as green and the chassis which I marked as red.
Blue being the control lead battery and ground.
Don't let this sloppy drawing that looks like the FM lead goes to the big post where we get the chassis battery, though! It actuall brings ground down but the wire is also connected to the mounting screw for the solenoid and THAT is also ground on most RV.
Just not a really plain item the way they drew it??
Click this snip to get a better view or go direct to get the full picture?
Neat system that does some really nice things but it also tends to be a pain as the contacts in the solenoid tend to burn and fail more often than we like!
Good thing to be aware of for future times if the coach batteries stop charging while we drive??