I know everyone says the drag is minimal, but I guess my assertion is that the weight of battery packs is just as minimal and cheaper. My plan is to avoid all AA and AAA devices where possible and use USB rechargeable devices. The lumen ratings of USB lights seem to be plenty comparable to hub lights and don't turn off when you stop pedalling. I suppose runtime could be an issue if you're doing really significant night time riding, but in Banff on the 10th Civil Twilight hours are 4:40 AM to 10:45 PM. We'll lose about 2 hours by halfway and maybe another 45 minutes by the end, but that's still lots of daylight. I don't see myself doing more than a couple hours of nighttime riding.

Also, I'm not sure I see a reason to modify a SPOT to be rechargeable. For one, rechargeables run at a lower voltage and SPOT clearly says they must be lithium. Rechargeables are way heavier and there a good chance that one fresh set will last the whole trip anyway. My gen3 with tracking on went through about a set per month over the course of 6 months on the AT. Maybe it's different with the gen2 though

Does anyone know of a write up comparing the wattage drag of a hub dynamo vs the weight of just carrying batteries? I've been digging around a little and dynamo hubs seem to put out around 3W. Add in the drag and and electrical losses and we're talking close to 5W. This is pretty much continuous since at such low power you'll probably charge electronics all day and at night would be running a dynamo light.

For carrying batteries the weight would also be constant. It would come down to how many lbs can you carry for 5W. I played around with some numbers on here: http://bikecalculator.com/examples.html and I think it's close to 1 lbs/W. It depends on your speed, grade and total weight. I went with what I thought were realistic numbers for me, which is surely on the slower and heavier side. I also only looked at positive grades, 5-8%, which from the elevation/grade profiles posted here should be higher than typical (not worst case, but accounting for most of the harder stuff). Riding it on flat ground would have even less of an impact and downhill should even recoup a good fraction of the energy.

Being conservative, couldn't you carry 5 - 10,000 mAh and still come out ahead? I found Aukey 10,000 mAh fast charging battery packs for 8.8 oz. And 50,000 mAh is a lot! The lot of them would only cost $125, meaning cheaper than a dynamo setup. What am I missing here? When does a hub dynamo actually make sense?