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My Audi A6 C6 always shows (through MMI) that my battery level is 100% despite if it's almost empty. Wondering how does it work? Does it only checks the voltage of the battery? If so wouldn't it be 100% whenever the engine is running? Maybe anyone knows what can be wrong because I see 100% even if the engine is stopped.

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    I would say the battery voltage is fed into an analog-digital converter connected to a microcontroller unit via some divider circuit. The microcontroller should be programmed to interpret anything over 12.6V as 100%. If the multimeter shows below 12V and the MMI still shows 100% then there might be an electrical fault, for example a bad ground to that circuit. It might be much more complicated than that, just my guess. Jan 11, 2016 at 17:17

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I found the answer in this manual.

Basically, the Battery Management Control Unit uses:

  • current draw on the battery (measured at the control unit)
  • temperature of the battery (measured at the control unit and transformed by algorythm to what the actual battery temperature should be)
  • voltage of the battery (measured at the positive terminal)
  • operating times

The software then makes an elaborate calculation to determine the battery's state of charge. If you are always at 100%, I would suggest that either your battery management control module is defective, or one of the sensors is defective.

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