My Forerunner will last about a week with 3 or 4 tracked runs. The lights for the pulse reading are on a lot. Once in a while it will pop up 'low battery' warnings, but I've always had enough to finish my run. Maybe there's some settings that will improve matters.
!BEER
I probably have something switched on that consumes battery such as the "Smart IQ" something or other that is meant to detect what exercise you are doing automatically but when I am at my computer it seems to think that my typing is the same thing as doing an elliptical so I think I should just switch that off.