can't you reduce the brightness on the Hotshot? I recall the max runtime for flashing on the original hotshot was 56 hours. I'm pretty sure I have used the throbbing setting on my hotshots for overnight. I have also recharged from a battery pack, doesn't take too long. But it would be a good idea to have a spare.
I hate Cygolytes website, why would the only source for runtime be the box, which everyone is going to throw away?