just a suggestion Mark, if you are wanting to use so many SLA batteries, why nopt just get one large 7Ah or so 12v SLA that alot of heavy weights use? link the speedos directly to that and away you go!! it will last for AGES, no problem with you weight as you say and much simpler to wire everything up??

oh yer, Ians maths is probably a little on the fuzzbuzz side. considering each gold only weighs 800g my gearbox weighs less than 100g leaving alot more weight. I think the limit is 1m cubed isnt it? though. why you building to feather sizes?