Yeah, my current hella usb adaptor has 0.8A and 2.1A. The former is not enough to have maps and the phone maintain charge, the later does both easily, however the phone can overheat and power down!
Just be sure that whatever you tap the USB/Voltmeter into is switched as the static draw is significant and will shorten your battery life unless you are always using a trickle charger. DAMHIK!
I can say for certain that it is, because the voltmeter is only on when the bike is on. Incidentally, the position of mine is good because the bars obscure it, so the blue LED voltmeter isn't distracting at night. However, you may want to give some consideration to keeping rain water out, as it can get quite wet in that area if the rain is heavy.
