I just got a case from PunkCase for my Note 20 Ultra and it actually has a built in 6000mah battery, which allegedly gives it 120% more juice.
It's a bit bulky, but in the few hours I have had it on, it hasn't really bothered me. Yet.
I figured I would give it a shot since I used phone a lot at work, and I could use a backup battery that is a little more convenient than a standard power bank.
Def