Pony bottles wouldn't last that long. Spare air would also burn out even quicker. They say a 13 cuft pony is supposed to last 30 minutes for childrens SASY rigs, but in reality, 15 is normal. 63 cuft cylinders would be a better choice. Also most backpacks won't fit pony bottles due to their reduced diameters. Most are made for diameters of 6" on up.