It is one vehicle, my X3 with a second battery used for a in car fridge. The whole point, it is a remote monitor of battery voltage. I can check the state of both batteries from 15 - 20 metres away, maybe more. No need to open the door, turn the key, start the head unit, enter a secret menu or get a multi meter. Things are more simple in the southern hemisphere.

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Neil

2016 X5 3.0D
2009 X3 3.0D
2005 X5 3.0 Diesel Sport (sold)
2007 320i (sold)