I have seen a lot of people argue you must use a 45W output power bank, probably because it’s the charger output Valve recommends for continuous play.
I have yet to pass 30W during play (admittedly I play with 100℅ brightness, not 120%). It will charge at a miserably slow rate, but if I start a session at full battery, I also end the session with a full battery.
If you own a 30W power bank already, it is not some strict requirement to upgrade it for the frame, just make sure to use the right output port.
21Wh battery, around one hour lifetime. Yes, it must obviously have a 90W draw!!
Good to have a number on the max draw. Honestly, assuming a slight loss at the buck converter I think at peak consumption a 30W charger might actually struggle. It will be a close call at any rate, but I wouldn’t be surprised if you went down to 99℅ after using it for a while. The horror!