2nd battery not charging T6.1 Coast

[WelshGas]

Sorry to hear this @Coasterman. It look like I have likely the same issue on a coast that is 4 weeks old. I have been away for the last couple of weeks and pretty disappointed with the battery life (2 days or so down to 12.3v with the fridge set to 3 and not really using anything else). I did notice at full charge the voltage of the front battery measured 12.9 or so but the control panel itself was only showing 12.6/12.7 when fully charged so this may be a pointer to the issue.

This thread prompted me to get into the rear battery and I am seeing 12.78v above the cube fuse (front battery probably not quite fully charged) and 12.35v below. I managed to get the battery out and the fuse is blown - probably has been since I collected it I guess. Local VW centre cant look at it for a couple of weeks so I am going to just buy fuse from them and give it a shot as planning to go away again next week. Couple of questions if I may hijack your thread since all the infos here.

I was going to recharge the battery as you suggest @yossarian to reduce the differential a bit. Positive from front battery is removed and taped up. Should I charge via the other side of the shunt to include the battery monitor or directly on the battery itself? and do I need to disconnect the 2 pin connector to get it to recalibrate afterwards? Worried about upsetting the control panel..

Also I am not the best at gauging tightness so any advise on how tight to make the positive when I get the new cube fuse and reconnect front battery as understand they are easy to crush?

You could charge the rear battery, but with a voltage differential of 0.43v there shouldn’t be a problem.
If you do recharge connect the -tve to a chassis earth, battery clamp bolt, or downstream of the shunt.
Could take 4 hrs or so for the battery monitor to recalibrate.

With regards tightening up the +tve lead I normally hand tighten then 1/4 turn with spanner.

 

[yossarian]

It looks like the 6.1 uses the data stored on the sensor. And based on @Morsels experience the sensor resets quite rapidly once the plug is disconnected.

I'd charge the rear battery if possible first and use the chassis ground. If it's not possible, as @WelshGas says, the soc is not terribly far out. You are probably looking at 50ish amps declining fairly rapidly. Not ideal but not the end of the world.

If you can, always connect downstream of the shunt (not on the battery) to avoid weirdness.

Edit: As an aside, according to the wiring diagram, both sensors are powered by the front battery (and the rear sensor incorrectly detects the front battery's voltage). So disconnecting the +ve on the front battery will reset both sensors if S339 is blown. However the next photo shows a sensor wired directly to the aft battery so at some point VW has changed this wiring.

Edits: rear sensor reading front voltage. Sensor reset with front bat disconnected.
Consider S339 blown / not blown.
Note on wiring difference to diagram.

 

[Ferryman]

Thanks all. Picked up fuse from vw this morning part #7h7937629a if it helps anybody. Charged battery installed fuse and now on van hookup all looking good I hope

 

[Loz]

I hate those factory battery terminals as it can be very easy to touch them on the case of the charger and the insulator nut is very brittle.
I swapped it over to this type as the cable then connects at the rear where there is more room and it improves the clearance between the battery and the charger.
Worth doing if you are changing the fuse anyway.

https://ebay.us/3bSUZr

 

[Private_Kelly]

Sorry to hear this @Coasterman. It look like I have likely the same issue on a coast that is 4 weeks old. I have been away for the last couple of weeks and pretty disappointed with the battery life (2 days or so down to 12.3v with the fridge set to 3 and not really using anything else). I did notice at full charge the voltage of the front battery measured 12.9 or so but the control panel itself was only showing 12.6/12.7 when fully charged so this may be a pointer to the issue.

This thread prompted me to get into the rear battery and I am seeing 12.78v above the cube fuse (front battery probably not quite fully charged) and 12.35v below. I managed to get the battery out and the fuse is blown - probably has been since I collected it I guess. Local VW centre cant look at it for a couple of weeks so I am going to just buy fuse from them and give it a shot as planning to go away again next week. Couple of questions if I may hijack your thread since all the infos here.

I was going to recharge the battery as you suggest @yossarian to reduce the differential a bit. Positive from front battery is removed and taped up. Should I charge via the other side of the shunt to include the battery monitor or directly on the battery itself? and do I need to disconnect the 2 pin connector to get it to recalibrate afterwards? Worried about upsetting the control panel..

Also I am not the best at gauging tightness so any advise on how tight to make the positive when I get the new cube fuse and reconnect front battery as understand they are easy to crush?

Hijack away. That’s what these threads are for imo. It’s all good stuff and very helpful. My van has now been at the garage for 3 weeks. Upshot is they are going to replace the Camper Control Unit.. I hope they put one of the old LCD ones in ( at least they worked ) The new and ”improved “ one is big pile of dog ****. Looks great tho. I have been trying to complain about this to VW consumer services but man alive how bad are they.

 

[yossarian]

I hate those factory battery terminals as it can be very easy to touch them on the case of the charger and the insulator nut is very brittle.
I swapped it over to this type as the cable then connects at the rear where there is more room and it improves the clearance between the battery and the charger.
Worth doing if you are changing the fuse anyway.
View attachment 82143
https://ebay.us/3bSUZr

Yes, as I found out today. Destroyed the nut over torquing it while trying to eliminate a 4 Ohm resistance at the fuse. Unfortunately the T6.1 needs an additional unfused connector on the battery terminal so I will stick with the OEM setup.