Negative battery terminal connection issue

[Blackberry66]

Hello. I have recently fitted a Bluetti Charger 1 into my 2016 T6 Caravelle. Both the Bluetti instructions and help on the Bluetti forum say to connect the cables to both the positive and negative terminal of the starter battery. Since doing this I have started to get issues with the van struggling starting and the battery going flat after a week. The battery is only a year old and this is happening despite the circuit breaker for the charger 1 being switched off once the van is parked up. I've seen a few posts on here saying that I should not connect anything to the negative terminal of the battery but not sure why and wondered if I should have connected the negative to a ground point instead. Can anyone offer any help and advice on this please?

 

[n10n]

You should not connect anything directly to the battery negative pole. Connect all negatives to the chassis / ground points instead.

The reason is the battery management - T6 calculates battery state of charge by measuring current through the negative lead, and adjusts alternator accordingly. If you connect any loads or chargers directly to the negative pole you bypass the measurement and the battery management will get confused.

 

[Blackberry66]

You should not connect anything directly to the battery negative pole. Connect all negatives to the chassis / ground points instead.

The reason is the battery management - T6 calculates battery state of charge by measuring current through the negative lead, and adjusts alternator accordingly. If you connect any loads or chargers directly to the negative pole you bypass the measurement and the battery management will get confused.

Great information thank you. I had a feeling this was the case but all the Bluetti people telling me its fine on their vehicles and that was the way I should do it.

 

[n10n]

There’s usually even this subtle hint on the cover of the negative pole

 

[Blackberry66]

There’s usually even this subtle hint on the cover of the negative pole

View attachment 268717

Unfortunately, I dont have this on mine

 

[t0mb0]

Despite not wanting people to use the battery terminal, VW completely fail to provide a very accessible ground point close to the battery on the T6…

 

[n10n]

Despite not wanting people to use the battery terminal, VW completely fail to provide a very accessible ground point close to the battery on the T6…

It’s crazy isn’t it?

Mrs n10n’s Q3 from 2015 has a mighty chassis connection point right next to the battery in plain sight for this very reason - so VAG group is not even consistent.

 

[Blackberry66]

Would you say my best option for a ground point near to the battery would be the headlight fixing bolt?

 

[t0mb0]

Would you say my best option for a ground point near to the battery would be the headlight fixing bolt?

Um, maybe! I know people do use that, but when I measured mine it had rather high resistance to ground so I don't know how reliable they are.

 

[n10n]

Would you say my best option for a ground point near to the battery would be the headlight fixing bolt?

The best option would be a proper ground point, there's one in scuttle bay behind the battery and couple low below the diesel filter. But they're quite hard to reach unfortunately.

Personally I've used the headlight fixing bolt, I cleaned little bit to ensure a good contact and measured the resistance to negative pole to be very low, about 0.002 ohm afair. I've had no problems charging through that.

 

[Blackberry66]

The best option would be a proper ground point, there's one in scuttle bay behind the battery and couple low below the diesel filter. But they're quite hard to reach unfortunately.

Personally I've used the headlight fixing bolt, I cleaned little bit to ensure a good contact and measured the resistance to negative pole to be very low, about 0.002 ohm afair. I've had no problems charging through that.

I will try the scuttle bay then thanks