Is it a battery and what I think is for?

[specware2020]

Howdy all,

In preparing our motorhome for an impending trip, I went under the chassis on a creeper looking for potential troubles yesterday. That was when I noticed, for the first time, what appears to be a presumably 12V auto battery, mounted at a rather peculiar location – behind the Onan Genset. The tray/bracket on which it sits is bolted on the inner side of the truck main frame under the chassis, hence one would never see it unless he is directly underneath the chassis and look up. The battery is connected and seems to be in service - the negative wire is terminated on the chassis frame, but I couldn’t trace where the positive wire goes.

The motorhome in question is a 2020 Coachmen Freelander (model 22XG) on 2019 Chevy Express 4500 chassis. I could not find any information regarding this battery anywhere, including the user manuals for both the Chassis and the coach. I am not sure whether it is integral part of the Chevy cut-away chassis, or it was installed by Coachmen afterwards. If it indeed is a battery (and I am quite sure it is) then, in addition to the one located in the engine compartment (behind the passenger side head lamp) and the coach battery in the stepwell, this would make the third battery for this MH.

One logical explanation I could think of is that this battery is there for the sole purpose of starting the Genset, as I have been wondering about from where the Genset draws power to start its engine, and this might explain it. If so, that it being tugged away deep in the chassis belly suggests to me that it is meant to be left alone and forgotten, i.e. not a maintenance item. Given the battery's deadweight and its awkward location, I am afraid that servicing or replacing it may not be a pleasant chore…

I am intrigued by this discovery and now am curious about its existence, I thought I would post my question here and hope for some confirmation. Does anyone have any idea?

Thank you all for your insights.

BTW, I did take a few photo shots of the underside chassis and wanted to share so you can get a better picture of what I was talking about, except, I don't know how to post them here without sending them up into the WWW.

[specware2020]

ron.dittmer wrote:
So...as I understand this, the purpose of this 2nd chassis battery is to power your chassis-related accessories like your in-dash stereo when the ignition key is in the accessory position, installed to avoid draining the engine-start battery?

In the case of Chevy Express cut-way chassis I believe that’s the general idea and the purpose, although I think the 2nd chassis battery is not used to power the in-dash stereo or any other cab installed equipment, which are all subject to the ignition switch cutoff, in ACC position, or in RAP(Retained Accessory Power) mode.

Referring specifically to my vehicle/MH, there are two cigarette lighter sockets (there is no built-in USB ports in the cab) and one 110VAC power outlet on the dashboard as DC/AC power sources. The 110VAC outlet is also switched like others mentioned above. But the two 12VDC sockets are always hot/on. While I have not disconnected either battery to verify, empirically I concluded that the two in-dash cigarette lighter sockets are the only ones connected to this 2nd battery, and the rest are still connected to the engine battery.

This arrangement may seem overkill, but for other (chassis built) applications, such as Shuttle bus or Ambulance/Emergency vehicle, perhaps they could find better use of this option/feature.

,

[ron_dittmer]

So...as I understand this, the purpose of this 2nd chassis battery is to power your chassis-related accessories like your in-dash stereo when the ignition key is in the accessory position, installed to avoid draining the engine-start battery?

[pnichols]

carringb wrote:
The location of the battery is most likely a result of the limited FAWR.

Ford offered this option too but it went below the passenger door. It took me a long time to discover it, and even longer to discover it dead. And yet even longer to discover it was never even hooked up because the original dealer never removed the removed the shipping jumper that isolates the aux battery. But it works great now! Only took 200,000 miles to figure it all out!

I'll bet that Ford option's wiring is present on the E350/E450 cutaway van chassis that Class C coach builders actually use to switch the solenoid ON that hooks the coach batteries to the engine alternator (so they will be charged when driving) whenever the ignition switch is turned to start the V10 engine. :h

[paulrichter]

Das ist wirklich cool!

[pnichols]

Why would this additional battery be needed in a motorhome that already had a boost switch on the dash?

[carringb]

The location of the battery is most likely a result of the limited FAWR.

Ford offered this option too but it went below the passenger door. It took me a long time to discover it, and even longer to discover it dead. And yet even longer to discover it was never even hooked up because the original dealer never removed the removed the shipping jumper that isolates the aux battery. But it works great now! Only took 200,000 miles to figure it all out!

[specware2020]

Newbiecampers wrote:
My 2018 Coachmen Freelander 21qb has the same frame-mounted battery (on a 2017 chevy 4500 express chassis). I spent a bunch of time in '18 trying to find out what it was. Like you, since it was near the generator, I thought it was a starting battery for said generator. However:

It is called the "Isolated 2nd battery" option. Isolated 2nd Battery — allows 2nd battery to be used when the vehicle is not running without affecting ability to start the vehicle ....

That’s it, Man!

I feel like I was drilling and drilling, and hit the oil reserve!! How did I make it prior to the time of World-Wide-Web and on-line forums is beyond me…

Kudos to @Newbiecampers for providing this much sought after information.

Now it all makes sense; Chassis manufacturers usually don’t like RV makers to mess around with their chassis lest it voids their warranties, so this hidden battery has got to be part of the vehicle features/functions.

This explains the other peculiar Chevy truck/chassis behaviors I observed and was puzzled by. For example, the two DC power ports (i.e. cigarette lighter) on the dashboard are always present whether the key being in or not. The first time I realized it was when I reviewed the dash cam recordings caught me to and from the restroom at a gas station. The 115VAC socket next to them, however, is on the engine switch, prompting me to think that the inverter is hooked up to the engine battery.

Well, mystery solved and my curious mind can rest. Thank you all.

[BruceMc]

Depending on the coach manufacturer, the house batteries may be behind an access door along either side of the coach, or in the step well just inside. Our Sunseeker has two group 27 12V batteries in the step well.

The extra battery is a GM option, and as Newbiecampers stated:

"Without the engine running, when you turn the ignition key to the very first accessory position, this frame-mounted battery will be powering the accessories instead of the battery in the engine compartment used for starting. "

Thus, this battery may or may not be in motorhomes based on the 4500 GM chassis.

It is this conversation that I've learned of the possible existence of an auxiliary battery on the GM 4500 chassis.

[pnichols]

There's something that I don't understand about this discussion. :h

Is it that Class C motorhomes built on the Chevy 4500 cutaway van chassis don't have the usual coach battery storage areas included by the coach builder that hold one, two, or three or more batteries to power the coach when camping?

I doubt it, hence .... why the need for some kind of "extra" battery hung off the Chevy van's frame?

My Ford E450 cutaway van chassis based Class C just has the usual engine battery under the hood, and a battery compartment built into the coach structure that can hold two large batteries for the coach.

However, on the dash is a rocker switch that switches the power for the cab radio between either the engine battery or the coach batteries. This allows the cab radio to be used when camping for listening to radio stations or CD music - since the cab radio output can be routed to speakers in the coach.

The cab 12V outlets on the dash are always-hot and powered by the engine battery. The 12V outlets in the coach are of course always fed by the coach batteries.

BTW, since the the 12V outlets on the dash are directly connected (through fuses) to the engine battery, when on hookups or in storage one can plug a solar or other kind of battery charger into one of these dash 12V receptacles so as to keep the engine battery charged.

[BruceMc]

While out in the barn, just in case I missed it... I checked under the Sunseeker. Mine is not equipped with the extra battery nor the bracket. It is a 2015 chassis, but each upfitter can specify different options on the chassis.

[BruceMc]

I wouldn't know, specifically, but it does have the generator fuel pickup in the tank. I've been into the pillar behind the drivers seat as the switched chassis battery connection to the BCC (Battery Control Center) was incorrect - the chassis was not charging the house batteries when the engine was running. It has the heavy cable routed from the chassis battery to the BCC, but the control wire never sensed the engine run condition.
I learned of this location by chasing the wires, then researching, I found upfitter-bodybuilder documents online for GM chassis:
BODY BUILDER MANUALFOR 2015 CHEVROLET EXPRESS/GMC SAVANA ELECTRICAL SECTION.

This document contains a reference to the Auxiliary battery:

G305 - Left center outer frame rail,near the auxiliary battery

So I've learned something! Yea, that would be nice to have a third battery, tho as others have mentioned, it's a maintenance nightmare. We purchased the Sunseeker in October 2015 and have enjoyed several boondocking nights but we tend to travel between those events, thus charging the house batteries (after fixing the sense wire issue).

Based on this document, I have a 159 inch "14,001–16,000 lbs/Hydraulic/Commercial Van or RV Cutaway" chassis.

[Newbiecampers]

BruceMc wrote:
Good information, Newbiecampers! I have the Chevy 4500 chassis under our 2016 2250 Sunseeker, and have been under it a number of times. I don't have that aux battery (fortunately?).

Hmmm, not sure if the Sunseeker branch did not order their bare Chevy chassis with the RV package, or if your's is prior to the extra battery becoming an option that came with the RV package, or....?

I am glad I have that battery. I dry-camp/boondock/camp without hookups almost exclusively, and I have been using that battery almost like another house-battery system in conjunction with my smaller inverter to charge numerous things, run the tv and dvd player etc..

[BruceMc]

Good information, Newbiecampers! I have the Chevy 4500 chassis under our 2016 2250 Sunseeker, and have been under it a number of times. I don't have that aux battery (fortunately?).

[Newbiecampers]

pnichols wrote:
One of my concerns about a battery mounted in that place is - how are you going to maintain it's water level and periodically clean corrosion from it's terminals? And just as importantly - how are you going to ever remove it and lift another one up in there to replace it? Being mounted there almost dictates that it be an AGM battery so no servicing is required ... but AGM batteries are just as heavy at replacement time.

I wonder if this is similar to the setup that (Chevy?) used to mount this additional battery?:
https://www.etrailer.com/RV-and-Camping/Tork-Lift/TLA7727.html

See my previous post.

And to service the water, you would basically need to use a mirror to see the top of the battery. There is not enough head room to sit up under there and see the top of the battery. Hence the reason I haven't touched it in three years.... ha ha.

I'll have the Chevy dealship deal with it when I have the camper in on their hoist for my every now-and-then dealership oil change.