I think the total number of 'affected' users is 90M.
The reason for this is they KNOW of 50 million, but there are an additional 40 M logged out "just in case".
I hope you see this, or if anyone can answer I'd appreciate it. Where does one go to research battery technology? What are the reputable journals? What is the discipline that is primarily motivated with researching battery technology?
To answer your last question, chemical or electrical engineering mainly, but chemistry, physics, and material engineering are all involved as well. There's no specific "battery tech" major, you can dive in with any partially related background.
I guess you answered your own question. There is a cart/horse problem with VR/AR. The tech isn't quite there, so no one wants to buy it, and people aren't going to improve it unless the money is there. And since people aren't buying it, the money isn't there...so the tech isn't quite there...