8000mAh can jump start a car and it can do it about 3 times.
As from its full capacity of 8,000mAh, you're able to jump-start a car about 3 times if you wanted to.
However, just something to keep in mind is that you should have a good amount of power left with this power bank if you do expect to jump-start your car.
A battery can sometimes be too dead to jump start a car.
If the battery is not taking a charge enough to jump start the car then it won't work.
In that case you need a new battery.
If the battery is just dead then it should be able to be jumped started by another vehicles battery and alternator system.
But yes a battery could be shorted out inside because of a dead cell in the battery which means it won't take a charge and allow the vehicle to start.
If you jump start the car and it starts and then you drive the vehicle around for awhile and then shut the car off and then it fails to start again then your batter is likely dead to where it's not taking a charge and you should replace the battery.
It's recommended to replace vehicle batteries every 3 to 5 years to prevent being stranded.