Forum Discussion

specware2020's avatar
specware2020
Explorer
Nov 17, 2020

Is it a battery and what I think is for?

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.

28 Replies

  • Cables can be hard to follow. They do bunch them in one cover bc that battery needs a charge line from the alt, converter and/or solar panel.

    Is there room in the stepwell for another battery ? If not the mystery battery might be a second coach battery hooked up in parallel to keep things 12v but double the amps. That gives you more boondocking power.

    with both the coach and chassis disconnected does the mystery battery power up anything ?
  • wildtoad wrote:
    Does the RV have an Gen Autostart if the main/house battery gets weak? Could this battery be just to start the gen when main won’t do?


    @wildtoad No, it does not. It’s manual start (rocker switch Prime/Start/stop). Whether this battery could be the backup for the main I have no idea. I know for a fact that the generator can still start when the coach battery is disconnected (switched to off). So, maybe it is the backup battery kicking in, but I doubt it very much that my unit is at this level of sophistication.

    @dodge_guy mentioned that he never heard of a dedicated battery to start the gen. Actually I don’t know it for sure either, it’s only my guess. I had conjectured that the generator draws its power off of the truck battery, that is, until the discovery of this mysterious battery.

    Both Tom_M and bobndot suggested that I disconnect the battery and figure it out. While that would be straightforward enough, it may not be the easiest. As I mentioned in the OP, the battery terminals are not easily accessed and harder to work on when you lay flat on the creeper. Tracing the electrical cable run from the positive terminal is also daunting, if not impossible, as it is braided with other cables into a larger bundle that runs alongside the chassis. I was hoping for an easier way out – by asking. To that end, though, I was surprised by the seemingly lack of industry standards in this regard. It looks to me that all RV manufacturers do not use the same/standard practices in dealing with the power systems (hence us consumers’ understanding/perception of it is all over the place). I just hope my generator does not die on me before I got a definitive answer…

    Speaking of calling Coachmen for technical support, I’ve tried this route in a couple of (other) occasions before without any luck, in fact they never bother calling me back or replying my emails. I can try my luck again I suppose.

    Thanks for all your replies.
  • Does the RV have an Gen Autostart if the main/house battery gets weak? Could this battery be just to start the gen when main won’t do?
  • It makes common sense to do as suggested, disconnect the battery to see if the gen starts.

    TL makes a mount for an additional battery, usually for the house bank but it could be used to house a battery for whatever .
    I use a third hidden battery that is dedicated to operate my 12 tv. If you can, follow the cables from the battery to see where they go.


    Torlift Hidden Power Mount
  • Never heard of a dedicated battery to start the generator. Maybe it is a second house battery?
  • Disconnect the battery. If the generator won't start, you've figured out what it is for.
  • I think you pretty much answered your own question.