They really should mention in the manual that the motor should be running. Charging the Bluetti while driving on a long trip, fine. Trying to charge it after you’ve parked is a recipe for a damaged dead car battery. And even if you managed to jump start it, be prepared to buy a new battery soon.
Not all batteries are the same.
-Car batteries are designed to produce a SHORT term burst of Amps to crank a motor. They are built with thin lead plates. Drawing continuous current shortens the battery life, along with draining it too low. If you’ve ever had a car that’s hard to start, you know you only have a handful of attempts left before the battery is drained.
If you go parking with your GF in your parents car, playing the 8-track for hours, you might find the car won’t start when it’s time to go. (Ahem, or so I’ve heard.) Thankfully there were jumper cables in the trunk.
-Before Lithium batteries, Real storage batteries were heavy and expensive because they had thick lead plates. They were designed to provide continuous power, but you could not run them down too low. You also might kill them if you try to start a car, they are not designed to do that.
Having read up on liveaboard boaters (my plans to join them got shot down), they always have 2 batteries; a big golf cart battery to run all the electronics, comms, lights, etc. and an isolated separate starter battery for the motor. You can’t afford to not be able to start the motor in the even of a severe storm, illness, whatever emergency. The motor of course recharged both batteries, with maybe the addition of a gasoline generator to spare for long trips. But the unwritten RULE was to make sure the starter battery was always charged and ready, never used for anything else.