I'm experiencing about 2 to 2 1/2 hour battery time on the 680 using fresh alkaline batteries with some occasional turning on of the back light. I think the best I've ever done was 2 hours 55 minutes. The unit mercifully shuts down automatically when the batteries die, and keeps the files intact, which is a nice feature. I do have an external battery source, which I like, but it is not always possible to run it inside venues.
I wish the unit would give me warning of a few minutes before shutting down. My experience with operating the unit on one bar (of three) of battery power is that last bar can mean 30-60 minutes battery time.
Has anyone used lithium batteries on this unit to extend the battery run time?