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One reviewer on Engadget reported about 5 hours of battery life during what he characterized as normal use, including taking a few photos/videos and reading emails. I don't recall whether he made any effort to conserve battery life or not, but as with any other device I would expect you could squeeze out another 10-20$ battery life if you made a serious effort to do so. Of course, this would require some sacrifices as to how often you synch, use GPS, etc.
The battery is located behind the wearer's right ear. It's a big unattractive rectangle, which is probably why most of the photos you see don't show the wearer from the right.