Rude Nora 4
Filthy Edna 2
Edna battery box, the way forward !!!
The Edna battery box can accommodate 1 x 18650 li-ion battery (unprotected). Low cost and widely available.
Battery weight is on the back of the helmet, where it needs to be, and 1 cell means that battery weight on head is minimised. LED caving lights no longer need massive 4 cell battery packs to achieve lots of light for lots of time.
I personally have a knackered neck thanks to years of using heavy helmet battery packs.