Keith
Technology exists to put a nice GPS in there, but the cost wold not be marketable so you can assume that every corner was cut even those cannot be cut, so most probably the antenna will function well enough inside a RF test box to pass, but its not gonna work under tree canopy hanging from your pack.
As phat pointed out - the battery is the kicker - how long will it last, how much does it cost, can it be replaced at all, can it be recharged, does it lose all memory when its replaced? I would assume the least cost invilving answer to each question. that is: <img src="/forums/images/graemlins/crazy.gif" alt="" />
not long, a lot, yes with a special tool, probably not, most likely yes.
So there you have it.
Jim <img src="/forums/images/graemlins/cool.gif" alt="" /> OR it might actually work - let us know. Start by trying it inside a metal file cabinet and see how far you have to open the drawer to aquire a signal. If it works in the closed drawer or slightly open - then it might work in a pack under trees.
<img src="/forums/images/graemlins/grin.gif" alt="" />Jim <img src="/forums/images/graemlins/cool.gif" alt="" />