Received the converter today. I don’t have a way to measure current ATM. So I did a runtime test :). I used 3 Panasonic NCR18650 cell to directly drive the projector, it gave me about 35 minutes before it started flickering and the cells were and 3.5V under load. With the converter the cells were down to 3v after 40 minutes. So no point of using it with battery pack. Might still be good for a car though.
According to HKJ Tests the remaining capacity at 3.5v is 15-20% so the efficiency is at 80% ballpark?
It gets very hot fast, I used a PC fan to cool it down and at 17C ambient temperature it was still quite hot to the touch