I had kind of assumed it would just trickle charge constantly rather than doing what it's doing? Charge was defo going in, but I'm going to struggle to get anything more than a little top up from the dynamo when on tour.
I would say you're going to struggle to get much charge out of the dynamo.
This is where it gets very annoying that everything is measured in mAh rather than watt hours.
My 10000mAh battery pack I got in ikea yesterday (€17 with a ikea family card...), has a more useful capacity rating of 37Wh.
At max output, a USB-WERK takes the 3W 6V AC and produces a 5V DC 500mA/2.5W output.
37/2.5, gives 14.8 hours to fully charge it. That's assuming you're going fast enough for the hub to be outputting 3W. Which depending on the dynamo might be a faster speed than you cruise at, esp if fully loaded touring.
The largest power pack Anker sell, their Powercore II 26800 is 96.48Wh (To be under the 100Wh max for taking on an airplane). At max output of a 3W dyno hub, and max output of the USB-Werk, is going to be 38.6 hours.
Usefully, said 96.48Wh pack has 2 2A inputs, allowing you to charge it twice as fast when you do get to power. This may be worth considering for those who are worried about getting a power pack fully charged over night in a hotel.
I see people talking about "surely it doesn't matter if your phone charges slow". But I've found having the option to put a load of power into the phone is really useful, as is having small packs you can have plugged into the phone, charging it in your jersey pocket. I have my phone playing podcasts or music at me when I'm cycling, and it doesn't have the battery life to go a whole day doing this. So I have need to be able to charge while I ride. Downside of the larger heavier packs is it becomes awkward to carry it in the jersey pocket for prolonged periods of time. On the plus side, hydration ports on packs can double as a place to route out a usb cable to plug in...
J