Preparing to upgrade engine battery power flow

Sail and the wind is the best source of power on a boat but second to that electrical power is critical not only to run the lights and chart plotters but to start the engine.  In 2006 I installed a new battery bank to assist the house bank.  It involved running a new set of battery wire from the new bank to the switch board and then rewiring the main switch panel.
Malua always seemed to lean over to Starboard because the main battery bank of six 6 volt 200Ah are located under the quarter berth on the starboard side.  The choice for the new battery bank was easy - it had to be on the port side.  The only reasonable place was under the aft cabin bunk so that is where it went.  I could only fit four 6 volt  Sonnenschein SB6 200 amp-hour batteries into the space.  No matter this bank drives the electronics and does not need as many amp-hour as the primary bank.

In the process I took the starting battery out of the circuit but left the cables running to the main switch board.  I estimated that the combined power of the 10 batteries would be sufficient to start the 50Hp Yanmar with ease.  In fact it is more than I require but on starting the engine the power draw leads to a drop in voltage to the chartplotter and it does not like it especially if the battery voltage is low.
The solution is to reintegrate the starting battery into the main switch board unfortunately the starting battery is not the same as the house batteries and therefore they have a different charging regime.  I cant just add the starting to one bank.  The starter will be connected directly to the starting bank and then add a switch to the cable from the generator cable to the main house bank and the starting bank.   To start the switch will be on starter, to charge switched to both or main bank.
Well that is the plan, all I have to do now is cable in the new switch and test it when Malua is back in the water.