I can confirm the same problem.
45min play time (3-4 round in BG) and the battery lost more then 50% of capacity.
Before BG patch I played 3-4hours without losing the 50% of battery capacity.
(environment: iPhone XS with IOS 14.0.1)
The heating problem is easy sensible.
So I think there is a problem with computing optimization, or do you mining bitcoin? 
Please have look on the issue!
Best Regards