Hi,
This is my second x728 (1st wouldn't charge). The x728 works great when plugged into a 5V power source, but when I switch to batteries, the rpi 4 seems to boot, but there is barely any power going out. 5V leads read at ~3.5 and the USBs on the pi read as ~0.3. I'm using two Samsung 36G 18650 3600mAh 10A Batteries. Any ideas, or do I have another faulty board?