Are the two leisure batteries independent?

[Sigurd]

Hi!
I have a couple of questions, that are all interconnected, regarding the two leisure batteries in T5 Comfortline:

1.The two batteries are often referred to as being connected in parallel in various forums (also this one). But the usermanual says that the first leisure battery (under the seat) provide the fridge, lamps etc. while the second leisure battery provides the auxiliary heater. That means that they are NOT connected in parallel while providing electricity to the equipment. Are they connected in parallel (while providing electricity)?

2. The display in the roof is said to show the status of the leisure batteries (plural). But this makes, to me, little sense if the two batteries are drained by different equipment (and are not connected in parallel). It does not make sense to display the COMBINED status of the two batteries if they are drained independently. Does the display show the combined status of the two batteries, ignoring that the actual status off the batteries are wildly different? Or does it display the status of only the first leisure battery?

3.I have read in several forums that the two leisure batteris should be the same size. But, again, this makes no sense if the two batteries are independently discharged. As I understand it, the two batteries are only connected in parallel when they are charged. But the charger must then handle batteries with very different discharge statuses. This would again mean that it should be okay to have different sized batteries (e.g 80Ah under the seat and 100Ah in the back). Is it, or is it not, ok to have different sized leisure batteries?

Hope anyone can help, because I am thoroughly confused.

 

[WelshGas]

Hi!
I have a couple of questions, that are all interconnected, regarding the two leisure batteries in T5 Comfortline:

1.The two batteries are often referred to as being connected in parallel in various forums (also this one). But the usermanual says that the first leisure battery (under the seat) provide the fridge, lamps etc. while the second leisure battery provides the auxiliary heater. That means that they are NOT connected in parallel while providing electricity to the equipment. Are they connected in parallel (while providing electricity)?

2. The display in the roof is said to show the status of the leisure batteries (plural). But this makes, to me, little sense if the two batteries are drained by different equipment (and are not connected in parallel). It does not make sense to display the COMBINED status of the two batteries if they are drained independently. Does the display show the combined status of the two batteries, ignoring that the actual status off the batteries are wildly different? Or does it display the status of only the first leisure battery?

3.I have read in several forums that the two leisure batteris should be the same size. But, again, this makes no sense if the two batteries are independently discharged. As I understand it, the two batteries are only connected in parallel when they are charged. But the charger must then handle batteries with very different discharge statuses. This would again mean that it should be okay to have different sized batteries (e.g 80Ah under the seat and 100Ah in the back). Is it, or is it not, ok to have different sized leisure batteries?

Hope anyone can help, because I am thoroughly confused.

The 2 Leisure Batteries are definitely wired in PARALLEL giving one large 12v 150 amp Leisure Battery.
A1 and A24 are the 2 Leisure Batteries. It is just VW's weird way of explaining things. The Leisure electrics are all connected to the Leisure Battery under the Passenger seat RHD battery A1, but this is intern wired in parallel to A24, the second leisure battery.

 

[Sigurd]

Puhh. Good to hear. It did not make any sense to me why VW would make such a complicated system with three separate battery banks. But the manual is REALLY misleading since it clearly states that the different batteries provide different equipment with current. AND it does not state anywhere (as I have managed to find) that the two batteries should be changed at the same time and be of the same size.

But I have a Norwegian manual, so the wording in the manual can be a result of bad translation.

The seller of California T5´s in Norway have been adamant that the two leisure batteries are totally independent. The result is that they gladly mix a new battery with a 12 year old battery and 80Ah with 100Ah.

 

[WelshGas]

Puhh. Good to hear. It did not make any sense to me why VW would make such a complicated system with three separate battery banks. But the manual is REALLY misleading since it clearly states that the different batteries provide different equipment with current. AND it does not state anywhere (as I have managed to find) that the two batteries should be changed at the same time and be of the same size.

But I have a Norwegian manual, so the wording in the manual can be a result of bad translation.

The seller of California T5´s in Norway have been adamant that the two leisure batteries are totally independent. The result is that they gladly mix a new battery with a 12 year old battery and 80Ah with 100Ah.

Here is a VW Training Manual for the T5.

 

[Sigurd]

Thanks, WelshGas!

One last question: when installing new batteries with more capacity (from 2*75Ah to 2*80Ah or 2*100Ah), should I reprogram something so that the capacity reading (%) in the display gets correct? Usually the system has to know the total capacity to accurately compute the remaining capacity.

I could not find any option for this in the non-public menu in the roof display, and there was no info on this in the manual you provided.

 

[WelshGas]

Thanks, WelshGas!

One last question: when installing new batteries with more capacity (from 2*75Ah to 2*80Ah or 2*100Ah), should I reprogram something so that the capacity reading (%) in the display gets correct? Usually the system has to know the total capacity to accurately compute the remaining capacity.

I could not find any option for this in the non-public menu in the roof display, and there was no info on this in the manual you provided.

No. The % Calculation is a very iffy calculation. It is best to ignore it and just depend on the Voltage, which is accurate.

 

[steve_b]

when doing anything with the batteries, always pay special attention to the cube fuse on top of the +ve of the rear battery under the wardrobe. because if that has blown (and it often has, as if people think they are independent) and let the 12v lead touch earth or chassis because they have removed the battery - but really it's still connected to the battery in the front - then your batteries truly are independent.

the front one does everything

the rear one does nothing due to the blown fuse

I plastic bag up every battery terminal when doing anything just to be sure.