LOL. I'd take a close look at those specs. At 50 Amp-Hours at 5V for $14.59. That's 5V x 50 Amp-Hrs = 250 Watt-Hours...or an eye-popping 6 cents per Watt-Hour. 
OK, I know prices have been coming down on these and I don't have one so maybe I have nothing to say...but geez Louise! I also see some battery packs claiming 100,000 mAH...or a whopping 500 Watt-Hours of storage for not much more $.
As to the charging issue. With storage capacities in the hundreds of Watt-Hours, you need to do-the-math. So let's say you indeed have a 250 Watt-Hour battery pack. And let's say you attempt to charge this pack with a USB 5V charger that puts out 1 Amp (typical for a $1 wall-wart USB smartphone charger). So the charger can deliver 5 Watts. That means it would take (at least) 50 Hours to charge a 250 Watt-Hour battery pack! So much for the idea of over-night charging. I guess that would be an over-weekend charger! 
OK, yes you can get 2 Amp or 3 Amp 5V USB chargers, and for all I know you can feed 12V from a car to charge these gadgets. I also figure you probably wouldn't wait for the battery-pack to completely discharge before re-charging. And so on. But the point is one must do their "due diligence".
In any case, I think rtr12 stumbled on a non-train technology which has great promise for our battery-powered applications!
