FYI: you can currently get a 30000mAh 65w Baseus power bank for £35 on Amazon : r/SteamDeck
Baseus Portable Laptop 30000mah Power Bank 65W Fast USB C in Nnewi - Accessories for Mobile Phones & Tablets, Dozzydata Teleglobal | Jiji.ng
Amazon.com: Baseus Portable Laptop Charger, 30000mAh Power Bank 65W Fast Charging USB C Battery Pack, PD 3.0 7-Port Battery Bank for MacBook, IPad, Dell, HP, Notebook, Switch, iPhone, Galaxy and More :