In looking around on the boards here I finally discovered why I've not been able to charge my Nook with my other home chargers, because it's USB 5.1 but I was wondering will it work with 5.0, just more slowly? I'm travelling and I'd rather just bring a single charger for my phone and Nook. Less things to lose that way.
The difference between 5.0 and 5.1 volts is irrelevant. But the HD wants a 2 amp charge current and normal USB power is only 0.5 amp -- USB charging ports can go to 1 amp when no data lines are active.