More Work on the Airshied

 I've tided up the battery mounting, replacing cardboard with aluminium sheet, made the contacts spring loaded and added a spring clip to stop it sliding out of the helmet! I've also taken off the outer shell of the helmet which doesn't really do anything except maybe stopping the filter bags snagging on stuff if you are working in a confined environment.
The unit now weighs a total of 1.58 lb against the original 2.4 lb which is a pretty significant improvement.
The battery life is a bit less, but I've measured the current draw(0.38A) and calculated it to be 2.95 hours which is fine for my usage, especially considering I have a second battery which I can just swap in.