I think we can be pretty sure that mech is not an RV owner! He is missing the basics on this!
This is a part of the RV wiring that is critical when we need to understand what it does as it is doing lots of things.
One of the big things it does it connect the coach and chassis battery together at times or disconnect them at other times.
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Looking at the parts I marked red, that is the chassis battery coming in to the mode solenoid. Solenoid is just a different name for relay or switch?
Chassis on one big lug and coach (green) on the other big lug. Blue lines are the control battery and ground that make this set of contacts close when we want them connected together at two different times/situations.
If we camp and run the coach batteries down a bit, this contact gets battery power on Wire LR when we start the RV engine. That battery makes the coil in the solenoid pull the contacts together as we drive and that lets the engine alternator put some charge in both the chassis and coach batteries! GOOD!
But if we find we have a weak chassis battery and the coach are still okay, we don't have to get out the jumper cables as we can use a dash switch for a "jump start"!
When we hold that dash switch battery is also put on LR! That pulls this solenoid and connects the two together for the jump start! GOOD!
If the RV is in a quiet spot, try the switch sometime? You may be able to hear the solenoid thump as it closes? With all the engine noise, we usually can't hear it as the engine starts. But if the coach batteries are charging as we drive, this is where it gets the power from the engine alternator!
Note that the coach battery (green) comes in on right and then goes to the coach battery disconnect? But that doesn't get involved with the chassis side unless the engine is running to connect them. That disconnect only disconnects some of the coach items, nothing on the chassis is involved there!
But see wire KKG on the left side of the solenoid? That is where the chassis side gets connected to the battery to feed power to lots of the chassis fuses. Just a convenient place to make the connection, I assume but if we want the chassis to work, we need this connected!
What the shop is missing is that we have to treat RV that we don't use often, different from we do our daily driver!
There are things on the coach and chassis batteries which stay connected, even if we open the coach disconnect! Safety items stay connected on coach. On the chassis there are things like door locks, ignition and radio presets which stay hot while we store.
It works the same on our cars and if we store the car for a month, we may come back to a dead battery! One of the things folks found when they started working from home and not driving to the office every day was batteries went dead!
The shop is not used to dealing with cars that are stored for a month or so!
Different ways to go to avoid the trouble. There used to be a Trik-L product but that business went out when the owner died. It was a cheap handy automatic thing to let a little power from the coach go to the chassis if we plugged the RV in when stored. No longer available but there are reports of a different brand but I have no info on that.
If we have AC power handy, we can plug the RV in as well as put a charger on the chassis battery? Kind of a pain and more junk in the way!
I have a place to plug RV when storing and have a different way to get charge from coach to chassis that fits me better than a standalone charger.
Somewhat crude and possible headache if I mess it up but simple?
When I drive home, both batteries will be a t near the same charge as they have been connected during the drive. The ony power needed to move from the coach to the chassis is the small amount to avoid the small drains like the radio running it down.
That is important as it lets me use a small gauge jumper form one battery to the other.
I don't need a big jumper cable because the current is really low!
On my last RV the coach and chassis battery were next to each other, so a small jumper with alligator clips from one positive to the other got it done for me! Negative is already connected together at the ground buss bar.
If the mode solenoid is handy, a strap between the two big lugs will do the same.
But this has a hazard involved if we are not alert! IF you forget to take this strap off and for some reason run one battery down while camped, the start /chassis battery will also be dead and you WILL be stranded until you get a real jump start!
Bottom line is that it is normal for RV to go dead while stored if we don't do something to avoid it!
Guys that get shipped off to basic training can find their battery died while they were gone!
