I want to chime in here that IMHO a forward windlass battery is a very bad idea. Much more effective are heavy gauge wires from the main bank. Here is the reasoning:
1. The charging
regime for the forward battery will require that it be disconnected from the main bank except when being charged (i.e. voltage over 13.8V). YOU CANNOT WIRE THE FORWARD BATTERY IN PARALLEL WITH THE MAIN BANK AT ALL TIMES or you will ruin both batteries.
2. With a forward battery, the main engine
cannot be used to provide additional, backup, or emergency
power to the windlass. This is a safety
issue. You need that windlass to run.
3. To properly charge the forward battery you won't be "trickle" charging. You will need fairly heavy gauge wires in any event -- why not save the effort of an additional battery.
An anchor battery sounds like a good idea at first; but it isn't. Keeping It Simple is running large cables