The experience when following a course while using Ultrac is pretty bad - because when it turns off the gps you get notifications of "Course lost!" and then when the GPS comes back on a minute later and acquires lock you are notified "course found!". This might actually use up more battery than is saved. Try it out on a course in your neighborhood. Remember that in this mode, the distance is solely from the watch accelerometer, so it doesn't work well if using hiking poles.
I generally don't take my 935 backpacking as the GPS battery life is pretty poor and normally take an old Highgear watch instead but am contemplating using Ultratrac for this trip instead. I had an old Suunto where I could set the tracking interval from 1-second to 10-seconds but the Garmin doesn't seem to have that ability.
Just how bad is Ultratrac?
ultratrac takes gps for 10 seconds every minute i think. i use it for tracking my sailing and what you see is intermittent good GPS tracks for 10 seconds and than 50 seconds nothing. fine for tracking, poor for navigating i would say.