I told you it was complicated. Now you want to get into the internal resistance of a cell phone battery compare to other batteries,
like C or D batteries. Do you know what internal resistance is ? Do you know the relationship between current and resistance as defined by Ohm's Law (E= I x R, P= I x E ) ?
Ok, you asked for it: don't say I didn't warn you..
Long story short: If the internal resistance is too high , then I = E/R < I (motor[min]) (The current is equal to the voltage devided by the resistance. In the case of the cell phone battery, the result of this calculation is a value of current that is below the minimum current necessary to drive the motor of the car. It might work for a second or two but I would be surprised if you are not loading the battery down so much that the voltage drops to almost zero until you disconnect the load. Did you try monitoring the battery voltage when you try to power everything from the battery ? Does the battery voltage drop drastically when you connect the motor and everything else ?