Had my Garmin GPS III for over three years and the only reason I'm getting the new GPS V is for the map downloadable capability mine didn't have. The base map setup is nice. About 100 tracklogs would be nice too if they'd get a clue.
The Duracell Ultra AA's work for twenty hours in mine and the processor in the "GPS V" consumes them at the same rate. The GPS III PLUS has the more efficient processor too but just lacks the pixell count and routing feature so the batteries will last even longer in this one.