I have a 2006 35' Baja Outlaw and last winter I completely rewired the battery system and stereo wiring. I am running with 4 blue top optima's. Two of which are banked on starboard motor and other two are banked on port motor. I have two switches that are standard for 35 baja. I used 4/0 cable for my battery runs from the switch to the batteries. The lengths range from 10-15 feet of cable. The motor ground wires are connected directly to battery banks grounds. The motor positive is connected to switch now(was previous connected to battery), so that I can switch from bank one to bank two if needed. My amp positive is also connected to the starboard switch. I also have the cuddy cabin 12-volt system (which only runs the fridge and occasional lights) on the port switch. This was to split load between stereo and fridge.

Now, my issue is that with batteries fully charged, when I run the boat WOT for 30+ minutes one of the banks, I get alarms that indicate low voltage. I know this because if i switch to ALL on both switches at this point the alarms go away. DO I NEED MORE BATTERIES? or what seems to be my issue?

PLEASE HELP, I spent alot of money on these batteries and was wondering if the BLUE TOPS are bad for my motors?

Are the batteries paralleled to each other ? what do you mean banked ? are you trying to charge both batteries off of one alternator

The #1 post on the port switch has copper buss bar going to #1 post on starboard switch. Each post on the switches has a battery lead connecting to its own battery, therefore with either switch on #1 I have 2 batteries in parallel.

Why do you have it hooked up like this You only need one battery per engine....

So each switch says #1 , #2 , Both , and Off ?

When alarm is sounding, do either of your dash gauges show less than charging voltage ?

You said amp is wired to starboard switch, but did not specify which post ?

Amp wire is on post 1. I thought having 2 blue tops would be better for long play times and other 2 batteries would be reserved for starting boat.

Gauges show good charge while running.

Just thought having 2 batteries in reserve would be good to start boat.

You said Post #1 goes to Post #1 of other switch ?

So if you are running on #2 of each battery bank - engines not tied together since they are if both on #1, you are draining power from that #1 switched battery the amp is connected to since it's not being charged.

First: You have an issue which is not the batteries, and that is needs to be determined.

Second: Optima Bats are crap IMO, but that is just me

Do you have one or two alternators?

Seems like you need to have the alt checked , then make sure each system is independent of the other, never combined. House power should be a stand alone system ,
You can afford to kill the house but not the starting batteries
If I read the diagram correctly you have the engines and alt system combined into one big single engine wiring system