Been for a few single track rides now, experimenting with battery positions.
1. The two velcro strapped batteries near steer tube are not secure enough for rough riding. Fine for the streets but no bumps allowed. They drop down and hit the top of the shocks.
2. I don't mind being tethered to the bike with two batteries in the back pack. It is by far the best handling on the bike, I feel I can really let loose downhill as they are very well padded up and suspended. Draw back, is my back. I get a sore back from mountain biking over lots of drops without a backpack, its only going to get worse the more batteries I carry there. Also they heat up more with tons of padding, no air and my back heat. Also I cant hear the alarms.
3. 6 batteries will not fit in my triangle, without a super complex shape and lots of wires being mushed together. The other problem is the brake and gear lines under the top tube taking up space and not allowing a triangle box to be secured there properly. Also the top of the down tube is very thin, weird organic shape. I wish I had squarish giant like tubes.
I am left with two last options.
a) similar to the velcroed position I get a custom 2 box saddle bag option near the steer tube. downside is high centre of gravity. Knees will get restricted in more aggressive pedalling.
b) a long custom box attached under the down tube, as its flatter underneath. downside is near the ground and nothing to else to attach it to to stop it swinging left and right.
ps The rocket frog downhill track has been manicured with beautiful dark soiled berms! Will definately get up there again, even just on a mountain bike.
psps Both my light holders snapped hitting almost imperceivable bumps. Lights kept working so easy to find them. One fell down a drain, which was hard to get while tethered to the bike.
. Will pull of the 3 way switch and see how much I miss it. Would be nice to unlcutter the handlebars as much as possible. 
