Sort:  

No it definitely wouldn't. That adapter can probably put a maximum of 50 watts out at peak load. Car batteries typically have around 45 Amp-hours of capacity (at 12V) if I'm not mistaken, so that's 540 Watt-hours at full charge. That's almost 11 hours of running the adapter non-stop to drain a car battery.

That's pretty accurate

It converts the power, so if you have 4 devices connected, it divides the power to those 4. So the outage is the same with 1 or 4 devices.

That's true :)