I've been having issues finding ways to charge my Insight handset, no matter what I've tried I can only get it to charge from a mains or car 12v socket where the USB power is less than 1W (or is managed).
I've never been able to use a computer USB or a battery pack when travelling.
I just recieved a SyncStop (from Amazon) and it allows me to charge my Handset from a PC or from a Mophie battery pack (when travelling away from mains or car power). These are available from the USA at $12.99, you may have to go on the USA Amazon site.
For those technically minded, this SyncStop acts as a buffer and makes the Handset think its plugged into a normal charger, it also reduces the charge power so may take a little longer to charge. I've tried it using my battery power pack and did not notice it taking any longer.