Sorry, a comprehensive guide to the tail lights has been on our to do list for a while in Irm towers( it’s a long list!)
You will need two batteries, one of top of the other.. It is a tight fit, but once you get a knack for it it’s easily done..
Just a tip for anyone that wants to add some to a 42ft flat, the dapol containers have removable floors, which makes fitting and threading the wires for the lights even easier.. I secured the light fittings to the sidewall of my container with double sided tape(€1.50 a roll in deals when I was buying the batteries) so they weren’t moving around in the container and the wires getting tangled..