I received my test kit this week. I have an Aukey 20,000mAh powerbank and a RAVPower 22,000mAh. When used on their own with a camera, the Aukey needs its power button to be pressed to deliver power to the connected cameras. However the RAVPower starts delivering power as soon as a device is plugged in.
I first tested the Kit with both powerbanks attached, and with 2No B1W cameras attached to the Kit's outputs. With 12v power ON, both cameras were running and both powerbanks were charging. However when I cut the 12v input, everything stopped.
So I tested it again with just the RAVPower attached. With 12v power ON, again both cameras were running and the powerbank was charging. When I cut the 12v input, the powerbank immediately switched to power output and both B1W cameras continued recording. Turning the 12v power bank on, the powerbank went back into charge mode and the B1Ws continued recording. This was with the car stationary, engine off but 12v circuit on. The left switch was in the DOWN position.
I moved the setup to the front of my car for the drive home so I could keep an eye on it. Same Kit switch settings, same powerbank. Outputs to A129 and Mobius 1. Turning on the Kit with its little button, both cameras started recording. When I turned on the diesel engine, the powerbank started charging, the A129 restarted, and the Mobius 1 attempted to restart but froze with solid red light. I unplugged the Mobius 1 from the Kit and plugged in a Mobius Maxi, which started recording so there was definitely power going to the M1 previously. When I arrived home after 30min the powerbank was still charging, and both A129 and Maxi were recording. However everything stopped when turning off the engine.
It appears that the Kit / powerbank behaves differently when receiving steady 12v power switched on/off, compared to 12v power with possible interruptions when starting or stopping the engine. Further testing needed....