Just taking a wild guess, without having to watch the 25 minute video, I remember reading something about a battery modification that required a change in the Spark software via DJI assistant on a PC to change a line of code to accept a non DJI battery in order for the Spark to respond to the change.
Search battery mods on this Forum and maybe find the answer, if that's the problem?
I had some time and watched your video for curiosity and it looks like the Spark received power from your get up at the beginning because around the 3 minute mark when you unplug it, the camera gimbal goes limp, indicating some power was there.
I'm not sure if this video will help, but I've watched it a few times and Rick, from Drone Valley gets very detailed about the battery and the engineering of it, like the power it provides and the arrangement of the pins.
On the YouTube channel, he has the video indexed in the comments section so you can go to a spot, if you find anything of interest.