Originally Posted by MYTraveler
I don't think it is a wiring problem with your thruster. If anything, inadequate wiring will reduce the current flow. Your electronics are shutting down because the voltage at the battery is getting too low because there is too much current demand, not too little. I am back to my original suggestion -- your batteries are weak, either under charged (verify that they are reaching full charge and that you have this problem when fully charged) or worn out (ie, significantly impaired capacity). You can confirm battery capacity with a load test. If they are proven bad, and if you have the facility, try equalizing them. Otherwise, I bet everything will be back to normal as soon as you replace the batteries. For what it is worth, lots of boats don't have a separate bow bank for the thruster and work just fine.
Inadequate wiring will increase the current draw as the wattage of the load is not changed and you will increase the draw by heating up the wiring while reducing the voltage to the motor (still requiring the same wattage draw) thus drawing more from the battery's.
It has been stated correctly that BT's should be wired to the starting battery's not the house as they are like a starter, demanding a high current draw for a short time, not what deep cycle battery's like to do.
Too small of a bank of brand new deep cycle battery's may not be able to provide the short term current requirements as the surface area of the plates is to low to provide the burst needed even fully charged and new.
The real difference between starting and deep cycle batteries is starting has more thinner plates giving a greater surface area for more current (more conversion area) in the short term. DC have thicker (denser) plates but less of them (given same size as starting) for longer low current production as their deeper lead plates provide more (slower but longer) chemical reaction between the water/acid conversion.
The BT and windless is mostly used when the engine is running so the higher voltage provided by the alt. actually reduces the in-use wire size amount by 15% so is a bit of a bonus (14.8v is 15% greater then 12.6v).
BT should be on starting battery's as well as the windless or a separate starting battery not on house or deep cycle.
BT must be wired with the proper cables or larger and all connections must be perfect and clean.