Dead Crank Battery

[Blindcoyote]

We leave our Thor Chateau 2017 29G Class C motor home plugged in, stored right next to the house.
It wouldn't crank at all, so I used the emergency start switch and got it running.
I could not find any appliance that was left on. I did find that the radio in the bedroom would not turn on at all, even when the "truck" motor and/or the generator was running. Could this be a source of battery drain?
2nd question: when you use the emergency start switch are you powering off the RV house batteries?
3d question: any other likely suspects for battery draining?
I realize that my crank battery might need replaced, but would like to explore first.
Thanks in advance. This is a great forum.

[Judge]

First, some Class C's do not charge the chassis battery when plugged into shore power. Your coach would need to have a Battery Isolation Manager that monitors both the house and chassis batteries and uses a microprocessor to determine when coach should charge the chassis battery when on shore power. You should get the schematics for your coach so you can verify whether you do or don't have a Battery Isolation Manager. It would be near your house batteries and could look something like the attached picture. Someone with your model can confirm whether your model has a BIM or not.

The chassis battery is not tied to the coach electrical system directly so only the house batteries are being used when you use 12V in the coach itself. This is done so you don't accidentally drain the chassis battery and not be able to start the engine.

When you use the Emergency Start Switch, it enables a relay to tie the house batteries to the chassis battery to boost it to help start the engine. When you release the button the relay turns off the the connection between the house and chassis batteries is broken.

You either have a bad chassis battery or something was left on like the parking lights, headlights, dome light, etc. I would put a charger on your chassis battery and then test it to see if it is bad.

[petefoss]

Not sure about yours,but my 31W class C doesn't maintain the chassis battery while plugged into shore power. Confirmed by Thor it's by design. So I plug a small battery maintainer into the AC oulet under the dinette and use a 12V plug into the cigarette lighter socket on the dash.

[petefoss]

FYI my chassis battery will drain in 4 to 6 weeks otherwise

[Lt Keefer]

In my last coach, a sob class c, the chassis battery would go dead in a couple of months if I didn't start it monthly.

[Trkyte@msn.com]

I would go for a bad battery. Your coach is a 2017,most likely on a 2016 chassis.
That means the battery is four years old. Just like your car how many years can you expect from it. Especially if it’s not run daily.

[Judge]

I forgot to mention in my earlier post.....

When I had my 2018 Outlaw 29H, the chassis battery was not charged on shore power.

I installed Trik-L-Start and it allowed my chassis battery to be maintained by the house batteries and charger.

http://www.lslproducts.net/TLSPage.html


It worked great and I never had to keep the chassis battery on its own charger.

[Chateauduchien]

That's what happened to me with 2017 26b Chateau. Battery shot, had to replace.

[IDguy]

Originally Posted by petefoss

Not sure about yours,but my 31W class C doesn't maintain the chassis battery while plugged into shore power. Confirmed by Thor it's by design. So I plug a small battery maintainer into the AC oulet under the dinette and use a 12V plug into the cigarette lighter socket on the dash.

Many (most) cigarette lighter sockets are not connected when the key is off. Be sure to verify.

[RVGeek]

I use a battery-mounted knife disconnect switch on the chassis battery ground post for storing the unit for months. With no parasitic drain on the battery, it will self discharge only 5-10 percent per month. I've never had a starting problem after storage.

These switches are available at auto parts stores for about $25. I would only use the knife-type due to the large starting current. Image attached.

Originally Posted by Blindcoyote

We leave our Thor Chateau 2017 29G Class C motor home plugged in, stored right next to the house.
It wouldn't crank at all, so I used the emergency start switch and got it running.
I could not find any appliance that was left on. I did find that the radio in the bedroom would not turn on at all, even when the "truck" motor and/or the generator was running. Could this be a source of battery drain?
2nd question: when you use the emergency start switch are you powering off the RV house batteries?
3d question: any other likely suspects for battery draining?
I realize that my crank battery might need replaced, but would like to explore first.
Thanks in advance. This is a great forum.

[Mr.Good]

My 2017 Thor Citation Sprinter did not charge the chassis battery when on shore power. There is a chassis battery disconnect on Sprinters right above the accelerator pedal. I found that current drains on the chassis battery include, the remote keyless entry, the dome lights and possibly the ECM as they say to wait 10 minutes after engine shutoff before pulling the disconnect.

I learned the hard way. Three months after not pulling the disconnect, the chassis battery was almost completely drained. The dome light would barely come on and when I tried to start the engine (diesel), there wasn't enough power to turn over the diesel. Finally had to buy a Schumacher XP750C booster to get it started. All this the night before leaving on a trip.

[petefoss]

Originally Posted by IDguy

Many (most) cigarette lighter sockets are not connected when the key is off. Be sure to verify.

Agree, I was a bit surprised and glad to find mine are. But that also means we have to remember to unplug chargers, etc.