Intermittent failure to start.

Almost no Class C's are set up from the factory to charge the chassis battery via shore power. A LOT of owners install a charger just for that reason. Google up "TRIK-L-START" to view an example. I installed that one and it was a breeze. There are others available.

It could be that your battery is faulty, but not likely ..... as new as it is. To rule that out, you may want to take your battery out of the rig and have a local parts house give it a load test. They do that for free.

Another option is to install a chassis battery disconnect ..... for when you are not going to use the coach for a few days (or for winter storage.) Amazon has at least a couple of styles. I will try to attach a pic of mine .... (may end up with just a link.) I open that switch just as religiously as I shut off the "salesman's" switch for the coach batteries. Never any "surprises" with that protocol. lol

Good luck with your fix ...... and safe travels.

https://photos.google.com/album/AF1QipPVZNDABfllStoPEY--AFTPvv4ZrxJkfFAtz95U/photo/AF1QipPmhoUdl-5d_7fwea8WxzGal1Oy94wvXcVjiS-T

We have an older (2007) Thor model. We've also had the battery go down, but not in 3 days.
The shore power does not connect to the truck battery.
I've heard that if you don't go out through the driver's door the little bits on the dash and stuff stay on. We once had the battery die because I left the GPS plgged into the cigarette lighter for 3 weeks.
I used to suspect that the heaters for the outside mirrors were switched on -- I didn't know which way was off.

When you reach your destination and setup, are you using any chassis electrical connections? This could be using some plug in inverter through the cab's power port or similar use? Are you connecting any 12 volt power directly to the chassis battery? Do you leave any chassis electrical systems powered up such as dash infotainment system, dome lights, etc?

Just wondering if there is some type of battery isolator that has failed. There usually is a steady current draw from the radio from it's keep alive memory, plus other things as suggested. If you get a clamp-on amp meter you can measure the current draw, you can also measure it with a voltmeter, then while you watch the amp meter pluck each fuse in and out till you see the current stop. That's the offending circuit.

TRIK-L-START

Before you do anything, make sure your battery cables are clean and tight.

My original thought was a bad solenoid if you have one installed. If you do not have one, install one. I was under the impression that Ford's had solenoids but I might be wrong. I always had to add one in GM's.

A solenoid will allow the camper (coach) battery to operate the camper while blocking draw off the truck battery.


From how you describe it, it seems like the camper is drawing down all batteries and the campers converter is only charging the camper (coach) battery.
Its common on TT's and TC's where the 7 way plug is left plugged in while parked overnight, allowing the rv to also draw off the trucks battery. By adding a solenoid it acts as if you were unplugging that 7 way power cord, isolating the truck battery.

Test the 'truck (chassis) battery' using an amp meter to see how much is drawing when its parked . Do not plug the camper into shore power while testing.
When the truck is off the amp meter might only read the radio memory from the truck radio. That's fine and is normal.
Have someone start turning on lights and fans in the camper and see how many amps you are using (if any) while you are monitoring things on your amp meter off the truck battery. See if the camper is actually drawing off the truck battery.

If you desire, your rv can be wired so the converter will charge all batteries while plugged in but only draw off the coach batteries, that's how mine came thru from the factory.

GGoodsell wrote:
On three occasions the engine has failed to start due to what appears to be a dead battery.

When you chase things like this based on "what appears to be", you often run down the wrong path.

First, You NEED an inexpensive digital multi-meter.......to be sure what the condition of the battery IS.

Often when new vehicles sit on the dealers lot for a LONG time before they sell (all kinds of vehicles), the batteries are neglected and they go bad just sitting there. This is especially likely if it is a conventional wet cell type.

GGoodsell wrote:
I'm looking for ideas - I have a 2018 Thor Chateau C class 28E motorhome. Any ideas?

Here's one. IMO, before you do anything, you need to check the resting battery drain by inserting an ammeter in between the chassis positive battery cable and the positive battery post to see what the static drain (all loads shut off in the coach) on the battery is. Post back what you find. You do have an intact factory warranty. If you start changing things, you risk voiding that portion dealing with electrical parts.

Chum lee

Does it happen at home, too? I'm wondering if you've got a vampire current draw - something that should not be drawing current when you're stopped, but does. Sadly, not all mechanics know how to check for this issue, but any competent mechanic should be able to.

Chumlee and BillHoughton nailed it.

Something is sucking power.