The Silverfish in my cruiser uses Panasonic cells, i have had the battery since 2019 and i can see no drop off in performance so yeah im a fan of Panasonic cells.
Arrow 9s use Silverfish packs, i think they usually come stock with a 48v 19/20ah, i think you will be fine with any name brand cells like Samsung,Panasonic or even LG!
Interior dimensions of the Silverfish will determine how many Ah, amp-hours, and the number of cells are held by the case.
You can check and compare measurements by using the above link. I don't have your measurements, but it looks like you'd be limited to 13S 4P.
Ask Jenny Mao!