Working on a power system for my SLR rig using RC batteries from hobbyking and the like. The goal here is to be able to accommodate multiple sizes of battery without swapping things on and off the rails or dealing with a complex lock system.
The hex holes are for running bungee cords through, the cutout slots on the back and bottom of the tray for running wires. You could also feasibly use a strap system.
Requires two M4 nuts, and two 24mm M4 bolts.
Hole dimensions calculated with:
y = 1.0155x + 0.2795 vertical
y = 0.9927x + 0.3602 horizontal