1999 270 DA with Twins and Generator Charging System Questions

[rowekmr]

I just got a a 1999 Sea Ray 270 Sundancer with twin 4.3l's and generator and it has 2 battery switches and 3 batteries with 2 wired in parallel. One switch has OFF 1 2 Both detents and the other is just ON OFF. I assume the one with ON and OFF is for the single battery which I assume is the engine's starting battery. The one with OFF 1 2 Both I assume is for the 2 house batteries.
My questions is with both engines running do they charge all 3 batteries at once or do they charge the starting battery first then switch to the house when the starting battery is full or ???
My house batteries are low underway at 12.5v vs 12.7 with engines off read with multimeter across the battery terminals. The single starting battery is 14v with engines running. I am thinking either the either (or both) alternators aren't charging properly or just I don't understand the systems.
This is with battery switch ON and the other BOTH.

 

[Hoplite808]

My 1996 270 has two battery switches too. One in the port side compartment and the other in the engine compartment. My setup is no generator with the single 7.4 motor. There are two batteries on the port side run parallel with each other to make them one large 12v battery. The starboard side battery is battery 1 on both switches and the port is battery 2. There is also a battery isolator wired in so that battery 1 receives a charge while battery 2 is selected but draws no power from battery 1.

The port side battery switch selects the battery to engage all the boat electronics with. I always select battery 2 (the house batteries) and only select battery 1 if the house battery dies as a means to start the engine.

The other battery switch in the engine compartment is to select 12v power to the inverter on my boat. That is all it connects to and serves as a service disconnect switch for that system. However if you leave this switch on both it will bypass the battery isolator and connect both batteries together. So a power drain to the house battery will also be a power drain to the start battery.

I would suspect that the on/off switch is likely the battery disconnect for the generator in your setup and the other should select the port and starboard battery banks to connect to the boats DC buss. Setting it to both should charge all the batteries if one is charging so I would suspect a fault somewhere if one set isn’t charging.