Looks like any USB C PowerDelivery (PD) power bank with 45w or more output should be able to charge it even while playing.. Anything less than 45w output will charge but lose power if you are actively using it.
I'm going to add that the math about the Deck having a 5200mah battery and thus with (let's say) a 25000mah powerbank it's easy to think that 25000/5200 almost 5 charges... that's wrong. The Deck has 7.7v battery while powerbanks normally are 3.6 so things don't translate directly.
Fastest way to know? https://www.steamdeck.com/en/tech/ The Deck has a 40Whr battery, a 20000mah powerbank should be around 74Whr and there the math is clear: less than two charges. Usually on the bottom of a powerbank there's the specs, should have that value too.
Thanks so much for this, it's what I really wanted to know.
Is the conversion from mAh to Whr something you can explain to a five year old, or should I really just search-engine that conversion if I need to in the future?
most will just slow the rate your deck discharges (if you're using it), you need a high output charger to actually charge it. Anker makes a few that will, i personally have the 737 and think its worth every single penny with the steam deck.
I can second this. I got mine on sale for $110, but even at full price it is worth it. With 140w of output power, it can even charge my Mac at full speed without issue.