It seems the ECU will operate down to 6 or 7 Volts. maybe one of the guys like @halifaxhops knows how much power they need but doesn't seem like much.
So take a worst case scenario during start, a battery that gets drawn down to 9 Volts and barely turning the starter.
Lets say the ECU is drawing 1 amp through the ohm resistor. V drop = 1 amp x .5 ohms, therfore the ECU is getting 1 amp at 8.5 Volts.
