Charging coach batteries from truck while underway

[Jim & Mary]

We just concluded a 1200 mile trip to West Yellowstone and back and it's evedent that the truck alternator is not charging the coach batteries underway. We only have the residential fridge running while underway, but during a day's drive the coach batteries still do not charge. When I got home yesterday, the inverter battery voltage read 11.6. I have almost 14 volts at the 7 pin connector in the truck bed when its engine is running. I have traced the wire to the 4 square box on the pin box, and then to the battery box terminal strip. The rotary switch is definitely on, as all 12V devices work.
Our batteries are 5 1/2 years old. (Diehard Platinum group 31 marine), I'm wondering if they're the problem. They will properly charge in the coach connected to shore power, as well as a portable automotive charger. Any thoughts for help?

Thanks,

Jim

[Shane Wood]

Jim
I would get the batteries load tested if 51/2 years old
More than likely the problem is they are getting weak
The inverter on shore power puts out a better charge than the truck can. The truck can only keep good batteries topped up while traveling

[Jim & Mary]

Thanks Shane, that seems to make a lot of sense.

[Ford truck guy]

Jim,
What Shane said..

I had that problem last year, was going from PA to VA and the batteries were dying... I check all connections, all seamed ok...

When I got home, I did a load test that proved my year old, “upgraded” batteries did not last very long... Replaced them with Lifeline, AGM’s.

[Blenhardt]

My 5 1/2 year old batteries are also not holding a charge even when constantly on a maintenance charger. I will be changing them this month prior to a planned trip.

[tangoparson]

Don’t just assume it is battery especially without some testing.

When i got my 36rl (used) the batteries showed full at the dealer lot. That of course was just seeing the converter output but the batteries were new.

When i got home they showed only about 1/4 charge on the panel. When I started troubleshooting a voltmeter at the batteries read full charge.

Following the advice of several on here, I focused in on the buss bar for the 12 volt system and found several loose connections. Tightened those and my low reading on the control center went back to normal.

That was a year ago. Just moved the coach a couple hundred miles after living in it for six months and have the same problem. Loose connections in the battery compartment will be the first check when i get to fixing this.

[r time soon]

While checking connections for tightness, be sure to check the connections for the battery disconnect switch also. Ours were barely finger snug and the nuts were loosening and probably getting looser with every bump while going down the road. We purchased our 2012 36RL in 2014. Lots of things to inspect and correct.

Chris & Maria

[mhs4771]

I had the same issue with the Battery Disconnect Switch. They were so lose that one nut was about ready to fall off. What alerted me was some strand indication on stupid little LEDs, flickering between Full and Empty.

[Jim & Mary]

Well, update

Took the two coach batteries (Sears Diehard Platinum Marine Group 31 ) 5 1/2 years old to a battery wholesaler in Tigard, OR., assuming I'm going to follow Joe's advice to buy two Lifeline AFM's. Both gents there separately load tested both batteries and found them "better than the published specs ". That begs the question, why in the world won't my F350 at least trickle charge while underwqay. The truck is fused for 25A and the fuse is of course still good. These two batteries load tested way better than good even for new batteries. I'm mistified.

Jim

[mhs4771]

Jim, when you were tracing the TV charge line, did you put your meter on the RW batteries with the TV connected and Shore power disconnected? Or even look at the Level Up panel, I know when I'm connected to the TV I can generally see approx 13.6 on the display. Just sounds like some where there is a disconnect between the charge line and the batteries.

[Mountainquilter]

We had the same problem and it ended up a blown fuse in the truck. We have a F350

[RW Cal]

Originally Posted by Jim & Mary

Well, update

Took the two coach batteries (Sears Diehard Platinum Marine Group 31 ) 5 1/2 years old to a battery wholesaler in Tigard, OR., assuming I'm going to follow Joe's advice to buy two Lifeline AFM's. Both gents there separately load tested both batteries and found them "better than the published specs ". That begs the question, why in the world won't my F350 at least trickle charge while underwqay. The truck is fused for 25A and the fuse is of course still good. These two batteries load tested way better than good even for new batteries. I'm mistified.

Jim

I believe the inverter draws around 10 amps @12v when idle. The fridge might take another 20 amps peak at 12V. My 2013 Ram 3500 supplies around 12 amps through the cable. Outside coach lights, brakes, tail lights, etc. will draw some as well. BTW, by hookup cable has a 12ga wire supplying the 12v. I believe 12ga is rated at 20 amps, so it doesn't look like Ram ever expected to be charging batteries. My mystery is why the inverter draws so much power when idle. I discovered this when I had to rewire the cutoff switch that did not cutoff the inverter. That was draining my new dual 12V RW-supplied batteries in less than 24 hours.

[Riverratt]

We had that problem so I switched to six volt AGM batteries. That solved my problem and they charge from the truck but even after six to eight hours on the road they are still at 50% or more. We only have the residential fridge on during the travel.