Long running GPS tracking

I'm going on a multi-day trip and I'd to record a (pretty-accurate) GPS trail. In this case, I'm less interested in using the other features of the watch, I just want to record a GPS trail for as long as possible. What's the best way to do this? I'm thinking "Track Me" with the UltraTrack option turned on? Any other thoughts? Any guess how long my battery will last?

Thanks.