GPS battery usage...
I recently returned from a trip to the BWCA, where I had my GPS on all the time that we were canoeing and portaging which was 4-6 hours a day for the four days we were out.
I usually use either NiMH or Alkaline batteries and expected to need a set of batteries for each day's travel.
My canoe partner suggested Lithium batteries -- and we completed the trip on a single set.