Seeing I will be out there longer than that, I need to find a way to keep my watch plugging along beyond 10 hours. My wife as a Garmin 405, so I could bring her watch and swap at the half way mark, but I like having all the data for the race in one activity.
I stumbled upon this website and thought I would give it a shot: Garmin 305 Battery Pak
I recently picked up this Duracell Instant USB charger and connected it to the 305 cradle/watch and then devised a way to attach it to my hydration pack. I took it on a four hour run on Friday, 12/24. When I returned and powered off the watch, immediately the screen showed the "Battery Charging Complete" message. Nice.
So for the race, I'll probably wait about 9 hours and then hook up my contraption for the last couple hours. I'll report back how it worked...and how many people told me I looked goofy.