Thanks for clearing that up, I may be totally ignorant about LED's but I'm getting there. (lesson 1: know not to mess with them, leave it to those who know....). It's a 29mm so that makes life easier.
Is the case back always part of the circuit, I thought I'd seen some modules that seemed to have clips attached to them by a screw. That would imply that the back isn't necessary to complete the circuit in that ..... case.
Having said that, I bought this watch knowing full well that the back cover was missing the battery connector. Can something as crude as tinfoil do or is that dangerous and daft. I ask because for about 6 years the fusebox on my Triumph Spitfire was only working thanks to a carefully placed piece of tinfoil. That got me around Ireland very successfully.