In this thread, apparently you can test a iPhone without a battery.
What about iPhone SE? Is it possible to check if the mainboard and screen is working by disconnecting the battery and then connecting the lightning cable to the mains?
The reason I wnt to do is to check if the lightning connector pins are damaged. By applying 3.8 V directly on the pins where the battery would have been connected and then pressing the power button, the phone booted up ( I see a current fluctuation between 0.15 and 0.72 A on the multimeter ) . But if I do try to power on the device just with the lightning connector, it doesnt. So, if it is possible technically to boot an iphone SE without a battery, then the connectors are damaged.