I'm having literally the same issue you are. Had to replace the whole unit cus the controller wouldn't turn on, second one same thing. And it's end of 2020 I can't believe the faulty battery issue is still happening, I'm about to just return this thing for a full refund.
I had a similar experience, brand new out of the box never used
I plugged controller into usb multiple charging hub and light turned to green in about 10 minutes indicating a full charge
Except it really was not charging opened controller and it went to red
Over an over same thing - was ready to return to seller
I found a post on this site maybe elsewhere that suggested plugging it into a a dedicated charger - so I used my my iphone brick into a wall outlet
Guess what... it fixed it and fully charged
after that it would take a charge from original hub, did not make sense
This was sometime back so can't recall all details, and unable to find post
I think I may have have opened controller so it was draining while charging
never had a problem since
Maybe worth a try... Hope it helps
Best