Replacing Batteries

I am going to replace batteries in my 2011 e2. Do you leave main switch off and remove one battery at a time or all six and make a diagram where all the wires go?

I change 2 at a time or make a diagram and change all 6. You really cant change 1 at a time cause you have to have the outside battery out of the way to get at the center.

Thanks that makes sense not much room