the wiring can be done in series or parallel, so i think a c sized li-ion could run all 3 in parallel. if they dont have closely matched vf they might not all be as bright but it would work, right? Oznog pointed out that the vf varies alot so maybe running parallel strings of series leds would work better (see below).
also, all these lumen calculations are based on the old rebel, once these tri-stars are made with the new rebels we will be lookng at around 660 lumens at 1 amp (around 220lumens each at 1 amp for the newest rebels). with 3 tri-stars mounted in a triple star mag, thats 9 leds, each as powerful as a cree Q5, with a total of about 2000 lumens. you could use 3 protected li-ion cells, and 3 parallel strings of 3 series leds, (not sure what reg board would work). in direct drive it would be insane for the first few seconds until your hand got cooked. edit: according to evan9162s measurements, at 1.5 amps the new rebel will put out 300 lumens. so in the first few minutes of direct drive the 9 rebel mag could put out 2700 lumens.
unrelated: rebels are great because they are cheap. if lumileds offered them on a star that was just big enough to allow hand soldering, for 50 cents more, the new rebels would be selling like crazy! it would be really cool if the star had the same footprint as a cree x-re emitter (without star). as it stands, its not worth the effort when you can get a cree Q5 star for $3 more. then again, i bet their main markets include people who have machines for mounting them. it would at least open them up to flashlight modders and home lighting designers.