I typically mount any COTI-type device to the side on the right tube--IMHO, that top-center alignment is the "ideal" setup (which is why most dedicated fusion goggles located the thermal sensor there), however most goggles will not have enough room to support a clip-on in this location, it just so happens that the TAD is just short enough, and the GPNVG format is just long enough that you can squeeze it in there, but it's a fairly tight fit, made possible in part because the bridge attachment point of the GPNVG optical pods is a little further "back" than most dual goggles:
I have not specifically tried the TAD / ECOTI on the BNVD-SG-UL, however it should be compatible with the PVS-14 bracket with some adjustment attached to the objective lens.
The TAD uses the same brackets as the COTI/ECOTI, and the PVS-14 bracket is reversible, so you would need to mount it "backwards" on the shorter RPO objectives on the -ULs to get the proper spacing between the projector and the lens.
External battery functionality is being finalized (hopefully prior to full release), and will be backwards compatible to the initial release TAD (i.e., not a new variant), and "split" cables are being discussed as well.
However, given how power hungry thermals are in comparison to analog image intensifier tubes, it may not be worth the squeeze to tie goggle power to the thermal capability, as you will be extending the thermal battery life by a small margin, but reducing the I^2 life by a much wider margin--this is a tough cookie for dedicated fusion systems to crack as it stands. At best it would be a situation-dependent pre-mission consideration.
~Augee