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.