Some computers (and we've mainly noticed this with Macs) limit the maximum power drawn from the USB port when prevents you from charging certain devices, including doppel. This is mostly happening when a laptop is not plugged into the mains (as the power saving mode blocks charging). It can also be related to the power saving settings of the computer. If you're charging from a laptop, try plugging the laptop in. If this doesn't work then using a USB plug-in a wall socket should work.