I have been using an AMOD gps tracker for my past few trips, and I have come to think that this is a great tool for my adventures. My goal is to provide both a gps log for inserting into my image metadata, as well as a graphical Google Earth representation of where I have been. My safari travelers seem to enjoy having these files as well.
The tracker runs off of three AAA batteries, which is less preferable to a pair of AA batteries, but I do get more than 15 hours from a set of Eneloop branded cells. I have set my device to create a log entry every 10 seconds, which seems to be enough data for me.
I left the unit on the hood of my Land Rover one afternoon, and the unit was eventually found on the ground 1km from where we were staying. The unit looks pretty bad, but still works like a charm. For $69 I will buy another one and this will be my backup.