Chassis battery won't turn over the engine

[RJ Schubert]

Hi Ted and others. I've got a similar situation to a post that was made in September 2024. Ted gave a good explanation on tracing down the chassis battery leads, and the hookups. I want to make sure that I've got things right before a trip in a few weeks.

When I was taking out the two house batteries for the winter, I did take a couple of pictures of the cables. Instead of my lead acid batteries, I just put in 2 AGM batteries. I switched my Renogy controller to Sealed (I think that is correct for AGM). The solar seems to be charging fine.

I have all light in the house, etc. I am plugged into shore power. My generator starts fine, and everything seems to work fine. Ok, so what's the problem you say? My chassis battery won't crank. When I jump it using the house battery switch, it starts right up. My chassis battery has just under 12 volts, and my two house batteries are just around 14 volts. One additional question that I have is does it really matter which positive/negative post to either battery the correct lead is connected? Is this true with the chassis battery as well?

I've attached some pictures. The solenoid is difficult to see because of the tight space. Any help in getting my chassis battery connected again would be much appreciated.

 

[RJ Schubert]

I forgot to add my motorhome to my signature line.

2018 Thor Quantum RQ29

Thanks.

 

[16ACE27]

Chassis battery below 12.o VDC is essentially dead. Have you tried charging it? It may have just coincidently reached its EOL. Nothing in changing house batteries should change the ability of the chassis battery to start the engine.

+ is + is +
- is - is -
when connected in parallel. There is some "minor" effect due to connection locations and battery interconnections that is often debated ad nauseum, but it really doesn't matter in the big picture.

 

[ducksface]

Your chassis battery has a surface charge.
It shows 12v(too low) until the slightest load is put to it and it drops to 9.4(ish) then immediately goes back to the false 12v when the load is disconnected.
Or it's just dead. Remove it and charge it off of the rv system.

Buy a battery.
Oddesey battery is the best bet these days.

Let us know what happens.

 

[RJ Schubert]

Chassis battery below 12.o VDC is essentially dead. Have you tried charging it? It may have just coincidently reached its EOL. Nothing in changing house batteries should change the ability of the chassis battery to start the engine.

+ is + is +
- is - is -
when connected in parallel. There is some "minor" effect due to connection locations and battery interconnections that is often debated ad nauseum, but it really doesn't matter in the big picture.

Thanks Ted. I'll go put a charger on it, and report back tomorrow.

 

[RJ Schubert]

Your chassis battery has a surface charge.
It shows 12v(too low) until the slightest load is put to it and it drops to 9.4(ish) then immediately goes back to the false 12v when the load is disconnected.
Or it's just dead. Remove it and charge it off of the rv system.

Buy a battery.
Oddesey battery is the best bet these days.

Let us know what happens.

Thanks Duckface. I'm going to put a charger on it tonight, and see how tomorrow goes. I'll also check the date on the battery. Thanks as always.

 

[Jimbo57]

How old is the battery and I think you should clean those terminal ends where they contact each other both negative and positive. Corrosion says 2 to 3 years old or older. Does this have 2 batteries in parallel because they should be replaced at same as the older battery will bring the new replacement

 

[PS89]

Not sure why you gave us photos of your house batteries when your concern is with the chassis battery, especially when the house batteries appear to be working correctly.

Let us know what the chassis battery does after charging. If it's original to the 2018 chassis, it's lived a long life already.

 

[GrandRover]

What is the CCA for the chassis batteries in a 2023 Thor Axis 24.1?

 

[16ACE27]

What is the CCA for the chassis batteries in a 2023 Thor Axis 24.1?

Without looking under the hood, I'd say 750 CCA for a 7.3 L V8

 

[GrandRover]

Without looking under the hood, I'd say 750 CCA for a 7.3 L V8

Sorry I was referring to the coach batteries.

 

[PS89]

Make sure you don't have the terminology for the batteries mixed up.

Coach or house batteries are of the deep cycle variety and do not have a CCA rating as CCA rating is for engine starting (chassis) batteries.

Deep cycle batteries are rated by storage capacity in Amp-Hours (AHr).

 

[16ACE27]

Sorry I was referring to the coach batteries.

There is no CCA for house batteries. CCA refers to a starting battery specification and the house batteries should ideally be deep cycle storage batteries.

 

[GrandRover]

Mine are lead acid, probably deep cycle. A friend tested them yesterday at his auto shop and set his tester for a rating of 600. He is also a long time RV owner. His tester said they are borderline and need to be replaced.
The two house batteries tested as 519 A and 524 A. He set his tester at 600 A as their rating.

My error on the CCA question. The engine battery tested fine at its 750 CCA rating.

 

[Jimbo57]

For testing I was told take the AH X 7.25= CCA.

 

[RJ Schubert]

Not sure why you gave us photos of your house batteries when your concern is with the chassis battery, especially when the house batteries appear to be working correctly.

Let us know what the chassis battery does after charging. If it's original to the 2018 chassis, it's lived a long life already.

I included the house battery pictures to ensure that some connection on that end was not misplaced and causing the problem.

Thanks

 

[16ACE27]

Mine are lead acid, probably deep cycle. A friend tested them yesterday at his auto shop and set his tester for a rating of 600. He is also a long time RV owner. His tester said they are borderline and need to be replaced.
The two house batteries tested as 519 A and 524 A. He set his tester at 600 A as their rating.

My error on the CCA question. The engine battery tested fine at its 750 CCA rating.

Testing deep cycle batteries with a CCA tester provides no useful information. You have to do a true capacity test which is difficult with FLA batteries as they are only supposed to be drawn down to 50% SOC.

 

[RJ Schubert]

Update to all: it looks like the chassis battery is original. It’s from Ford so unless a prior owner put another Fors battery in this one is from 2018. I am replacing it today. That should take care of my starting issue.

Thanks every for the feedback.

 

[ducksface]

Consider an oddessy battery.
No sadness.

Amazon.com : odyssey battery

 

[RJ Schubert]

Not sure why you gave us photos of your house batteries when your concern is with the chassis battery, especially when the house batteries appear to be working correctly.

Let us know what the chassis battery does after charging. If it's original to the 2018 chassis, it's lived a long life already.

Hi all. Final update. I bought a group 65 AGM battery and installed it. The motorhome started right up and is charging as it should.

Thanks again to everyone for all of the advice.

RJ