This thread has gotten me thinking, which is a dangerous thing. If it is beneficial to use a high CCA, thin plate battery for starting, would it make any sense to use the same kind of battery as a dedicated battery for a bow thruster? You would use it infrequently, relatively speaking, and if it was mounted near the bow, you would reduce the length of heavy wire required. Since I know almost nothing about bow thrusters, I may be asking a silly question, and if so, I apologize.
I was looking at wire size tables and to carry 500+ Amps (746 hp/amp x 9 hp/12v = 559 A), it would take 4/0 wire (or better, depending on length of run and tolerable voltage drop).