Help…..Frustrated Beyond Belief

If I'm reading this right, the dead battery is in the eco flow, not the car? If so, usually there's a fuse inside the cigarette lighter plug. I'd start there. Most plugs have the two sides held together with a small machine screw and nut. 8 amps draw should be fine for cigarette lighter sockets. I've found that a solid state fridge will wipe out my batteries (4) in my truck in 36 hours with the engine off.
The battery or charge controller in the eco flow might be bad, but that's beyond my level of experience.