2 years of data????
Here are direct quotes from two 305 owners:
GW --
The Edge 305 can store 13,000 track points. You can configure it to sample once every second, or use "smart recording", where it only stores a track point when triggered by a change of direction, speed, etc. In once per second mode, it will run out of track point storage in about 3.5 hours. In "smart recording" mode it will depend on how often a change triggers a track point store, but I've found it averages about one point store every 5 to 6 seconds on my rides, so I expect I could get around 20 hours of riding in before it would begin overwriting.
Certainly could be a problem on multi-day trips if you don't have access to a laptop.
Rob--
Hmmmm, now I can't remember how many days worth of data it'll store before over-writing. It's a lot, but I think after 4 or 5 days you'll have to download it. With my HAC4 I could only get 5 days, so had my wife meet me at the end of day 5 with my laptop. I just can't remember how much ride storage is there. (And part of that has to do with sampling, as well.)
Don't know how you'd upload to Motion-based without a pc.