Twitch,

Your theory holds true only for AC (induction) motors not DC motors such as starters.

The current draw on a DC motor will decrease as the voltage decreases. The output torque is proportional to the current and that is why the cranking speed decreases as the battery discharges.

AC motors draw more current as the voltage decreases because they try to put out the same amount of mechanical power. The motor speed decreases, the slip speed increases and the back EMF is reduced. So AC the motor draws more current, overheats and burns out if the low voltage is applied too long to an AC motor under load.

P E H