Running my MacBook pro off one of my DeWalt power tool batteries. There are USB-C adapters for most major tool battery brands out there, many of which (like this one) will both power devices and charge the tool battery from a standard USB-C power plug. YMMV in terms of quality/safety (this is the official dewalt adapter which works great).

Great for power redundancy, etc. A no brainer if you already have the batteries for tools.