I remember my first introduction to "modern" ECU's. I stopped to get gas and the truck, 2003 Ford Sport Trac, wouldn't even turn over when the key was turned. Nothing, not even a click from the solenoid. I couldn't understand how the battery could be that dead, and have happened so quickly. I was then informed that when the voltage drops below a certain point the ECU won't allow any action by the starter circuit.
I've had the problem happen several times since then, albeit with different vehicles and different people. I'm old school and had simply thought with old school thoughts that the engine will try to start until the battery is too exhausted to do much of anything. Not no mo.