The battery, even when brand new from iFixit, barely lasted an hour or two on Youtube while I am at work. Two videos around 15-20 minutes, medium brightness, 720p, and the damn thing barely lasted those two videos.

googles

This is a discussion from back when they came out, and it sounds like two hours is maybe about right.

https://discussions.apple.com/thread/2789298?sortBy=best

Maybe get a 100Wh USB-C power bank? It sounds like you can get USB-C-to-MagSafe adapters.