One 12v 7.0 Ah lead sealed battery.
One borrowed 'The 12V bible for boats' book.
One idiot with less electrical knowledge than a garden squirrel who still has to get a waterproof toggle switch, an in-line waterproof 2 amp fuse, some extra wire and some heat shrink tubing.
What could possibly go wrong?
Blog post and video to follow in next few weeks when it stops raining!