Atego 815 Main Battery Replacement

[Tasminracer]

Hi, all possibly a stupid question but how the heck do you get the battery out to change it. Do you have to remove the complete side rail, which looks like a pita as lots of rusty nuts and bolts or is there a clever way something hinges. the gap between the top of the rail and the body is less than the heights of the battery, even if you could find a way of lifting it in situ !!