That's correct. It isn't a pass-thru. You can charge from EITHER port. BUT I am surmising that if you have a low power charger that can only charge ONE BATTERY AT A TIME, you can use TWO low power chargers, to enable charging both at the same time. That is probably accomplished with a full-wave BRIDGE to get TWO IN'S to give ONE COMBINED OUT. I passed this by Rick at Drone Valley, and he is checking out my theory. I expect that he'll have an addendum to his review of the dual-charger soon.