I'd be curious to see if you could check the voltage going into the juicebox. I noticed that when plugging in my car at my brother's house, the amp meter he has shows it slowly steps up to the full draw. I'd suspect that something might be in place to reduce the draw if the voltage drop is too much (IE, 210v, 200v, etc).
Do you have a volt meter that you could tap into where your charger is connected? This is just a theory...
Do you have a volt meter that you could tap into where your charger is connected? This is just a theory...