Hopefully MobileQubes [0] or similar competitors become more prevalent, there's a convention I go to where the hotel has had these kiosks since 2015. You pay ~$5 to rent a fully-charge external battery for 24 hours, with whatever connector your phone uses, after which you return it to the kiosk. If you fail to return it you're automatically charged the "buy" cost.

Yeah it's not free, but it's really nice if you underestimated your battery life since you're not tied to a single spot while charging it.

[0] https://mobilequbes.com/