Without a light modifier, two sets of batteries got me through the entire runway show. I am on the lookout for more battery holders, but havent seen them, at least fairly priced, for ages.
There are indeed some good homebrew modifiers. My drawer lining plastic one is excellent, but only in a normal sized room. All they really do is increase the flash area somewhat, plus bounce some of the light, while sill maintaining a forward component to the light. It's great if the bounce component can actually be used, but not in a large convention hall with a high ceiling. I've since obtained the remote sensor for the 555, so will use a conventional cloth diffuser next time that still sends all light forward, to get the slight benefit of a softer, larger light.