Does this vehicle use two batteries? I have read about this message on an E class that used two batteries, the little one at the back of the car was bad (read very expensive) and some sort of giant relay was also acting up too - this giant relay was the contactor for this small battery.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)