12v DC out generator? That's weird unless its a cigar lighter socket on the side next to the USB port! .....Most are 110-120/240VAC and as been said in naseum, 240V will output half the amps as the 120V rating.Your 48V charger would step down 120V to ~52V charging voltage for the 48V (13.2VX4) DC with possible 2X the amps of the 120V. There is no free lunch when it comes to power....