Now a days it is getting common for cameras to charge the battery via USB, I plugged in an external battery (not fully charged) to the camera to see how fast it needed to charge the battery.
Almost empty battery, started charging at 14:57
73% charged at 16:07
1hr and 10 mins
I have heard that if you have the external battery charger, you will also be able to plug an external battery to charge the battery.