The only way that motor is going to run off of a car battery, is to have the vehicle engine running, of course, and take manual control of the alternator field current. You would need to allow it to have as much current as it can draw. In this case, which will mean battery failure, eventually, and maybe burn out the alternator, but you would most likely get the voltage you need to run the electric motor. Do I recommand doing this, absolutely not, unless it is an emergency. Even then, you have to really know what you are doing before attemping it. The 12 volt battery might turn the motor, very slowly. The amps being drawn might still damage the alternator, and drain the battery. This provided that no protection device opens up, cutting off power. That motor was designed toi run off of at least 90 volts, as you say. 12 volts, not even 14 volts which is what alternators usually generate to charge the battery is not going to run that motor. Due to initial in rush current (yes, motors do have what is called an In Rush current. Take a good look at motor specifications, you'll find it mentioned) you'll probably just burn something out. Remember, that motor is a dead short to the current supply until it begins to move. As it comes up in speed, it develops a reverse voltage which causes the current (Amps) to begin to diminish. Once the motor is at it's designed speed, the current needed for it to do it's job is all that is goiing to be drawn. If you want to see this in practice, get a variable power supply that will provide at least 100 volts DC with built in Amp meters, and volt meters. Slowly advance the voltage from the power supply and watch the Amp meters. Continue to raise the voltage until the motor begins to run. Note the lowest voltage, and the Amps that the motor will run at, with a load that will require at least 75% of it's rated power in Horse Power. You'll find out very quickly that this motor will just sit there like a big lump of metal at 12 volts and do nothing more than draw a lot of amps. A lot of Amps will not make up for a lack of voltage. Low voltage is what is known as "brown out" a term used by electric companies to describe a low voltage condition. It's a good way to destroy a motor.
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