Why doesn't the USB power port seem to charge my device?

The USB port can provide around 500mA, which is standard for high powered USB 2.0 devices; these are perfect for using a W3 or B1 for instance.

However, when trying to charge a iPad or iPhone for example, they require around 1000mA to charge with the screen on (the iPad's included USB charger actually provides around 2100mA to speed up charging with the screen on).  If your device is at a higher battery level it should work fine to plug it in to the USB power port to maintain the battery while listening to music (with the screen on it will always show "not charging").  If the battery is low though, we'd recommend plugging it into the charger that came with it.