I have a 21800mah (edit: it's 26800) Anker power bank from like 2015 that is by far the most reliable power bank I've ever had or seen. I have older and newer banks die, even others from Anker, but not that one. It doesn't have PD, only quickcharge 2.0 (edit: 3.0) or something, it's like a green label on that port. It's enough to sustain my Samsung ultra phone like 3-5x+ completely, still, after all these years. I do try not to leave it in really hot or cold places though, like in the car. It IS like a flat half of an actual brick, though, and the body is actual metal.

Looked it up, I think it's this one https://www.amazon.com/gp/product/B01K6TA748

I'm blown away that the product even still has a listing on Amazon, even if it might be discontinued (not sure). If you CAN get this battery, I give it (and only it) an absolute 10/10 rating. Just don't expect to charge anything like a laptop, Switch, or even a Steam Deck at normal speed. Phones, though? Chefs kiss.

Edit2: looked around a little bit, and it does seem to be discontinued. I wouldn't buy from ebay or a used one, but I don't think I'd sell mine. Not even for a thousand dollars. That sounds crazy, but when I need a reliable bank for a road trip or camping, having a really reliable battery pack is worth a FUCKTON of time testing and finding a good product, that I'm just not excited to try again any time soon. Reliability in something like this is worth a lot to me.