Topic: Chassis battery not charging from plug-in, solar, or generator . . . . (Read 2441 times) previous topic - next topic

Hi all,
We have a 2023 TB Unity. We have been home for about a month and the camper has been plugged in to shore power the whole time. The solar has been getting lots of sunshine too. Despite all that, the chassis battery has dropped to 12.4V. I just ran the generator thinking at least that would charge the chassis and still no effect on the chassis battery. Is this the expected behavior and my only options are to keep charging the chassis or disconnect its battery when we are staying in one place for a while? Is there some switch or fuse that I need to throw or change?
I just read the post by Gail - I can see that maybe the problem is that the Firefly system is not showing a correct voltage?

Either way, it still looks like maybe none of my coach power systems charge the chassis battery.
Thanks

Only thing that charges your chassis battery is your diesel mb engine, so you need to drive it.
When parked & have 120volts you could attach a trickle charger to chassis, or a small portable solar panel.
There few other ways, or disconnect the batteries.

Thanks Harry,
I really appreciate you getting back to me. I looked on the forums a little deeper and it looks like some people have installed the Blue Sea Battery Link ACR 7611. That device would do what I want to have happen. I guess it never occurred to me that Triple EEE would not have installed an Automatic Charging Relay (ACR) as part of the standard build. My 2003 BigFoot had an ACR as standard equipment so I thought all rigs had them. I guess I have another project for when I am next home for a stretch.

I have a 2018 Unity MB. While clearing snow off the roof recently I noticed for the first time what looks like a valve with cap you find on a wheel tire. It is located on the rear of the roof in close proximity to the shower sky lite. Anyone know the purpose ot it?

I was under the original idea that the house and chassis batteries were independent per the salesman on a used Unity.  Not so, under the passenger seat is a link that controls when the chassis battery is charge the house or the opposite.  Having changed this I still had non-communication between the two. 

Finally I asked the wiring diagram from LTV and it showed a 200 amp fuse which after looking about was adjacent to the chassis battery under the driver's floor.  $12 into Amazon for a dual pack and the time to replace it (not a difficult thing as long as you don't do all the unnecessary stuff like remove the passenger seat to change out the ACR (that whole discussion is in a previous post "Topic: BIM or other battery isolation in Unity").  That is the other place to look to get your batteries to talk again, didn't work in my case. 

I changed the fuse about 4 months ago and the batteries have been chatting to and fro happily since, much to the satisfaction of my house and chassis batteries.

So, leaving the shore power plugged in over the winter will charge the house battery but not the chassis, right? But if I install a Blue Sea ACR, then shore power will charge both?

That would work if the chassis and house batteries are indeed connected. 

Initially I had the LTV installed battery isolator present under the front passenger seat, thought it was faulty and changed it to the Blue Sea ACR on the recommendation of another owner on this forum.  I still didn't have the chassis and house battery talking, turns out there is a 200 amp fuse (sitting adjacent to the chassis battery under the driver's floor).  It had burned out and changing that reconnected the two batteries.  I of course did the repair the long way around with a number of nonproductive, but not too costly, efforts. 

So now while driving the chassis battery charges the house, the generator will in turn charge the chassis battery and when plugged in both batteries are under charge.  The ACR even allows you to add an indicator light to see if a charge is crossing between the batteries.  So, yes, I leave the RV plugged in over the winter (with appliances off I don't see a big difference in electrical cost--it is just plain to high regardless) and both batteries appear to be happy when I pull the RV out anytime through the year.

I have a 2022 Unity RL. It is true--the chassis battery only charges while the engine is running. Likewise I discovered that my battery would be almost dead after just two weeks of none use. I would need to hook it up to a charger to get it going again. I talked with Willie at TripleE (Excellent source for solutions of most of the problems offered up on this website) and he directed me to the MB operation manual. Here is what I discovered:
1. With the ignition on and the engine off scroll to "vehicle" on the main touch screen. 
2. Scroll down and choose standby mode.
3. The next screen will ask you whether you want to activate--CHOOSE the YES response. 
4. Turn off the ignition.
After a few minutes (15-30) the firefly display will read 0.1 volts. This should be good for approximately 26 weeks of non-use. I rarely go more than a month without starting the MH and have never had a problem using this method.

Mercedes sells a charger that I was told was compatible with the 2021 Sprinter chassis I have despite their software saying it was not compatible.  My Sprinter has a lithium battery under the passenger seat that is charged by the chassis battery.  My Mercedes charger never goes into trickle charge mode on the Sprinter.  It does on my Toyota.  So rather than leave it on, I check the chassis battery using the Mercedes ap.  I had an accident last year and the shop did not keep the chassis battery charged per the ap.  They told me they had to replace the lithium battery. When I see the chassis battery needing a charge, I use the charger.  Or drive it to a campground.