HairyFool
Member Since: 04 Jan 2023
Location: Essex
Posts: 535
  
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| Auxiliary battery purpose? |
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Looking at a D4 today and noticed that the auxiliary battery box had power leads going to it. Inside I find that there is a small LA battery in the front of the box.
The salesman claimed it was the start stop battery which of course it is not but how does it fit into the electrical system? I see on line that it is classed as an auxiliary battery but to drive what? A visitor from the dark side, my other vehicle is an MG5 EV
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 2nd Dec 2023 7:12 pm |
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Carl and Petra
Member Since: 13 Feb 2015
Location: Hautes Pyrenees
Posts: 199
 
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Without it your stop start system does not function so the salesman nailed it.
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| 2nd Dec 2023 7:25 pm |
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HairyFool
Member Since: 04 Jan 2023
Location: Essex
Posts: 535
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Strictly speaking no! There is no possible way that battery can start the engine which is what was being claimed.
Done some more digging since I asked the question. The SS system will not function if that battery is bad which is not the same thing.
The aux battery maintains some 12v services when the engine has been stopped (which ones is harder to find) preventing draw from the SS battery. If the Aux battery is bad the BMS knows it can't serve it purpose so the engine will not be stopped maintaining alternator supply instead. A visitor from the dark side, my other vehicle is an MG5 EV
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| 2nd Dec 2023 8:03 pm |
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Carl and Petra
Member Since: 13 Feb 2015
Location: Hautes Pyrenees
Posts: 199
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I still say the salesman nailed it.
I back this up with the fact that when our SS battery died the SS system also failed…ergo the salesman nailed it.
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| 2nd Dec 2023 8:32 pm |
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eightfoot
Member Since: 12 Apr 2015
Location: sunny essex
Posts: 762
 
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i think the s/s batt keeps everything working when the s/s shuts the engine off and then starts the car again when needed with the main batt so its not getting discharged when waiting without the motor running  (could be wrong though) please excuse any grammer/punctuation mistakes,i'm thick,thankyou
current vehicles 2005 d3 2013 d4
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| 2nd Dec 2023 8:44 pm |
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