I feel compelled to chime in that my 2nd Gen Arc is also not quite as bright as my Infinity. I don't have any means of measure this but my eyes, but at anywhere from 1 - 20 ft range the Infinity edges out the ARC.
With this in mind I tested the battery life, and with a new AAA Duracell Ultra I got over 20 hours in the bright mode, compared to the expected ~5 hrs! My test was not as "clean" as it could have been (turned it off twice for long periods while I went to work, and it actually died while I was sleeping so I don't have an exact number), but the result was impressive regardless.
Before anyone says "send it back", let me say that I prefer the longer battery run for my purpose, so I'm not complaining.
Gary