Most battery bricks will work, so long as they support USB-C PD or QC. I use one of each of these in varying circumstances:
https://www.amazon.com/gp/product/B08NRM8M35/
https://www.amazon.com/gp/product/B08NRM6X2Y/
No, it doesn't come with a case. I probably wouldn't use it for backpacking, but I do use it out of a backpack when on rail or foot wandering a city. And from my car.
So far it's working great, except that it sometimes switches SIM slots for no clear reason and I have to manually nudge it to get it back on cellular.
USB-C PD can negotiate 12V.
I use the 15V version of this to power my FIOS ONT.