[MPaulHolmes]

The 10v you are talking about is from Gate to Source, which makes sure that the mosfet is turned on. When it is below like 4v, the mosfet is turned off, and above around 4v, the mosfet is turned on. So, the datasheet used 10v from gate to source just to really make sure it was turned on. When the mosfet is turned on, the current from DRAIN to SOURCE can be 230 amps, and the resistance from DRAIN to SOURCE (RdsOn) is 0.0075 Ohms. However, the 9 mosfets would be on at the same time, so it would be NINE 0.0075 Ohm resistors in parallel, for a net resistance of 1/9*0.0075.

The mosfets don't really care what the pack voltage is (up to a point) since all that really matters is RdsOn and the current through the mosfet. If you stay clear of 200v, you are just fine! So, if you have a 120v system, the mosfet doesn't care at all. If you have a 12v system, the mosfet doesn't care.

Let's say we are pushing 80 amps through each mosfet. Then the voltage drop across each mosfet is 80*0.0075 = 0.6v. And the heat dissipated in each mosfet while it is in the ON state is 80*0.6 = 48 watts. Crap! What is this, a dang toaster oven?! OH well...