@Rocketman - you are right - a standalone AC battery charger in the Stern could move energy from the front battery bank to the rear battery bank in the same way the bow standalone AC Battery charger moves energy to the front battery bank from the rear battery bank. This transfer of energy can only done by AC chargers it seems (unless there is another way that I have no clue about at this time).
It CANNOT be done via DC UNLESS both batteries are at the same or almost exact same voltage - otherwise there is a MASSIVE INRUSH of current that would trip all the safety devices or burn the cables - it could be thousands of amps depending on the voltage of each bank. If both batteries are at the same or almost same voltage then what would be the point of transferring energy between them?
So it has to be an AC transfer method and standalone battery chargers are the only way I can come up with to do this. It cannot be the AC OUT of one inverter feeding the AC IN of another inverter.
I think we have this right in the sense explained above.
By having a standalone AC charger at each end of the boat, energy from each big battery bank can be transferred up and down the boat as may be needed. If the BMS on the stern battery bank trips, the front battery bank is still operational and Vice Versa. So that all makes sense.
I would think that an Automatic Transfer Switch of some kind would be the way to wire this up (and this is where the sparky does come in) so that if one of the inverters fail the other would be switched to automatically,
The whole logic of this thread is to make sure there is enough energy in the battery bank connected to the inverter (at either end, but the stern is easy since it is close to DC charge sources) so that when that Inverter is called upon to power an AC circuit there is indeed enough energy in that battery bank to make sure that AC circuit is powered up correctly.
There are going to be a number of AC circuits going from back to front and back again to wire all this up. However thats the benefit - its AC and the wire sizes are very manageable - we are only moving approx 5kW of AC energy 15 mtrs at most.
Definitely food for thought and worth chasing up a bit more. I think I need to go to logical diagrams next.
Been doing a ton of reading the last days trying to figure this out. Seems those Winston batteries might be the right choice for up front in the bow area- they are built very VERY solidly. I could use the EVE 304aH cells back in the stern area were everything is well protected and solid.