Yep you need help, the caps lock is on the left, above the shift and below the tab normally. Turn off the caps. Often considered yelling and not polite.
Anyway, I don't think you will find a 390amp car battery. If it's a small battery that is probably Cold Cranking Amps, Not the same as Amp hours. I think most of my car batteries are around 650CCA, I don't bnuy small ones unles it's all that will fit.
You should use deep cycle batteries, as an example of the diffence in AMP hours and Cranking Amps. I have a few LARGE deep cycles Trojan L16P series and they are only 360amp hours. They are about 2-3 times the size as a 650CCA auto battery.
You might be able to use a car battery but you will probably ruin it kinda fast. They are not meant to be drained much, they are built to always be charged, give a short burt of power and charge right back up.
As for using the batteries, I would not expect much run time before it goes dead.
Not sure myself how to figure the power you'd get from the motor. Half the volts, slower speed and maybe half or less the power I think. Not sure on that.
How you gonna run the car alternator?
