Ok I'm going all in then. I'm be getting a Tsunami2 2200 "Big Steam" version, a 5 amp Bluerail board with the external antenna and a basic 12V LiIon battery and charger from Amazon. If this all goes well, I'll probably invest in a 14.8V battery from MTO, but the price tag is a bit steep for a "try deadrail" experiment.
Worst case I'll just switch to AC track power. The battery pack I'm getting is large, but I measured the (Giant) tender and it should work.
I didn't opt for the big 4 amp Tsunami decoder, I just couldn't stomach almost a hundred dollars more. But the 2200 is rated for 2 amps, and I measured the stalled amps on my other big steam S1 with a similar motor at less than 2.
I'll start a new thread showing my progress, thanks for the advice you guys! Excited about getting into battery and remote!