Charging Circuit Speed Triple 2015

I'm after a bit of advice/tech help from any electrical boffins out there, especially those with go pro cameras used on the bike. I'm wanting to fit a go pro for my trip to Spain later this year and I'm wondering if it can be charged on the move or do you have to charge the batteries separate. I already have a cig socket wired in to keep the sat nav charged but I don't know if there'd be enough juice in the system to also power a USB socket to charge maybe 3 go pro batteries at the same time. The sat nav draws 5 volts, don't know about amps and I don't know what the go pro charger would draw but I would have thought being a USB it would be fairly small. Any ideas please. Cheers.
Ps I'm guessing the go pro is USB, they look that way in all the eBay ads.

 

Actually the more I think about it the system is designed to power heated grips so it ought to cope with the sat nav and a USB. The alternator is 35 amp. Still appreciate views on the go pro camera tho re charging on the move etc.