Going way up the thread to Russ' comment "I'm not a fan of using a GPS electronic compass (Geko 301) because they use a lot of battery.":

A while back someone at Groundspeak forums** did some power consumption measurements (in mAmps) using a Garmin eTrex Vista HCX with fresh alkaline batteries. Here are some of the results:

backlight off, WAAS off, electronic compass off: 69 mAmps
backlight off, WAAS on, electronic compass off: 70 mAmps
backlight off, WAAS on, electronic compass on: 70 mAmps
everything off - including GPS receiver: 98 mAmps (??)
everything off, backlight on: 235 mAmps (!!!!)

So from his measurements the use of the electronic compass made measureable difference in current draw. Pretty much the same for WAAS The backlight is the big battery killer.

Another person on Groundspeak did the same measurements with an eTrex Venture CX w/ fully charged rechargable batteries and found similar results - but couldn't measure an electronic compass since it didn't have one:

backlight off: 77.4 mAmps
backlight medium: 144 mAmps
backlight high: 220 mAmps
no measureable difference w/ WAAS on/off

I found this very enlightening.



**From http://forums.groundspeak.com/GC/index.p...p;#entry3123403