Originally Posted by Oscarguitar
It's more to do with the electric power steering on the six cylinder versions. It can draw a lot of current and if you are trolling you risk running the battery down below the current required to run the pump. So if you have two batteries and a VSR this shouldn't happen.
Also as stated the fly by wire stuff doesn't like low voltages so this setup helps to avoid potential problems
So it is a more technical set up but does allow you you to forget about the batteries (AMG recommended) on you have switched them on.
That's fair enough if you have to follow the engine manufacturers recommendations.
Just thought I'd mention for anyone considering not installing VRS that I run on both batteries in the "Both" position whilst the engine is running (Over 240Ah available). Only selecting single battery if using electrics whilst engine is off, thus protecting one battery for restarting.