Re: Bow Thruster problem
If you can physically drag a good battery and a set of jumper cables forward, one fast way to check things would be to be do just that. If the thruster spins up just fine, then you know there is a problem in the wiring. If it still is sluggish, that would point to an internal problem.
I've no idea what the voltage should run under load but I suspect 10V is way too low and that indicates a corroded connection somewhere between the thruster and the main batteries. Even a starter motor doesn't normally pull voltage down that low.
13V at idle is also low, a good alternator will be putting out 13.8-14.4 volts in most cases, and at idle with nothing engaged, you should see almost all of that even at the thruster. Another sign of a contact/wiring problem, check right at the batteries to see what the real drop is from "there" to "there".