Cali T6.1 Ocean leisure batteries are charging but starter battery isn't

[Tamasbako1978]

I'm having a wierd issue on my T6.1. Trying to find out whether the alternator or starter battery is broken and the finding is this (measured values):

- starter battery sits at 11.8v with engine not running and all accessories turned off (it drained a few times during winter and I removed it for reconditioning which seemed to work but I'm a bit puzzled now)
- if I start the cali, it fires up normally without any issues but battery still reads 11.8v

I thought that the alternator might have issues but the leisure batteries does charge:

- reading 13.2v when car is off
- 14.4v-14.6v when car idles (high idle cold start)

My assumption is that
A) the batter is shorted and doesn't charge - yet still it should read different with car running, even if it's shorted, right?
B) Something is bad in the wiring

- But since the leisure batteries are charging, I'm not sure whether replacing the starter battery solves anything or not... any experience or ideas anyone ?

 

[rod_vw]

Do you have the original factory leisure battery charging circuit using a simple split charge relay under the left front seat or has it been replaced with a modern B2B unit?
If you have the original circuitry then with the engine running the +ve poles of each battery are electrically connected together and should read more or less the same voltage.
If they are not then my initial thought is that the -ve circuit of the engine battery which includes the battery monitoring module could be faulty. To check that you should measure the voltage difference between the engine battery -ve terminal and a known good chassis ground. A significant voltage here would bear out my suspicion above.

 

[Tamasbako1978]

"If you have the original circuitry then with the engine running the +ve poles of each battery are electrically connected together and should read more or less the same voltage."

Not entirely sure, it's a T6.1 but quite a lot of hardware under the seat (battery and surrounding). I'll doublecheck tomorrow. Thank You for the tip.

 

[rod_vw]

"If you have the original circuitry then with the engine running the +ve poles of each battery are electrically connected together and should read more or less the same voltage."

Not entirely sure, it's a T6.1 but quite a lot of hardware under the seat (battery and surrounding). I'll doublecheck tomorrow. Thank You for the tip.

FYI here is a version of the wiring diagram which I suspect will be the same or very similar to yours if you only have one leisure battery (there are versions with two!)
This shows the electrical relationship between Battery A which is the engine battery and Battery A1 which is the leisure one. The battery isolation relay J7 which connects the leisure battery for charging is controlled by a signal from the Body Control Module (BCM) J619 and is normally active when ever the alternator is providing current.

 

[TripleBee]

You know you have 3 batteries?
One in the engine compartiment, one under the left front seat and one under the cupboard on the left in the back?
The one in the engine compartiment is the starter battery, the two inside are the leisure batteries.
What do you measure with a multimeter on all 3 of them separately? Not only looking at the display inside.
You know you have regenerative charging of at least the starter battery. This means, while driving and idling, the starter battery isn't really charged, but held at about 12,2V.
Try putting some load on the battery by putting on all the possible consumers (all the outside lights, airco on low, seat heaters, ...). Then the starter battery should be charged.

 

[Tamasbako1978]

Thanks for you both! I'll put load on it to check if it charges and yes, it's 3 batteries I have. I'll measure all three separate. Measured the one under the seat and that showed the same numbers as the control panel which was reassuring. The starter is the one that worries me as it didn't go over 11.8v but there was no load just idle and engine shut off. Will further experiment Today but this battery might be shorted as it was completely drained a couple times in the past 2 years and while reconditioning seems to work I'm not sure.