If the batter has lost its charge already, I'd imagine i will already be running like this.
It's probably not dead enough that the ECU would have lost it's settings, just dead enough not to be able to crank the engine.
Regardless, it's a bit of a moot point, as if you can't crank the engine, you can't drive it and see if it's idling erratically anyway

I honestly don't know how cars are even allowed to leave the factory with defects like this. It's 2018 ffs![]()
A lack of proper testing, I guess. The weak battery was never an issue for lots of owners, including me, who drove the car regularly. My car (2013 model) was perfect for 4.5 years and never failed to start.
The problem only cropped up when I stopped using the car daily - left it for just over a week, battery too weak to start. I've since bought a Bosch battery and haven't had a problem since, even when leaving it much longer.