snip

I tested battery life earlier this year by leaving on in tracking mode
on the dash of my car, and restarting it every 18-24 hours to ensure
it was operating 24/7. Sometime around day 12, the power LED turned
RED, and the SPOT continued to operate just fine for several more
days. So this means at least 300 hours of CONTINUOUS live tracking.
That's pretty much a typical season for a fairly active pilot.

The local grocery store sells a 4 pack of the batteries for $12 or
so. I'm sure they can be found elsewhere for even less.

Why on earth would you want to complicate things and add an external
power cord??? ;-)
snip

I didn't realize the battery life was this good. Replacing the battery
once per year would be ok.
Does it auto power off after a period of time? Especially if it can't
get a GPS fix like when the glider is in the trailer.. I can certainly
see me leaving it on and having dead batteries when I go to fly. Or
course I do always have spare batteries.

If it did have an external power supply it would be nice if it could
automatically power up to track mode when power is applied, One less
thing to remember to turn on.
It could possibly even be programmed to send a position when power is
turned off. LIke an external OK or Help button.

I like things that stay in the glider and I don't have to mess with
them until I need them.

More batteries I don't need. I already have a 9V in my B40 and 9V in
my EW FR 4 AA in my GPS, a watch battery and lithium battery in my
PDA. All are connected to my aircraft power supply.

Thanks for the info,

Brian