best way to wire 4 battery panel

I want to add two more batteries for a total of 4 batteries supplying the house panel on a boat. The circuit is charged through an AC battery charger (plug it in at home) and not the alternator. My initial plan was just to add two batteries to the circuit and wire them in parallel (see first pic).

I wanted a little more control, so I am planning on adding another manual battery switch (Blue Sea). Do you see anything wrong with how I am going to wire it?

Why or when will you use the switch - what is its function?

The reason I ask is that (IMO) they are normally used as a backup - ie, when it's too difficult to push start a car or boat.
And maintenance involves the ability to isolate the string of interest.


From a load POV there is the desire to have as many batteries in parallel as possible to increase EACH battery's AH capacity as well as increasing battery life (thru lower discharge rate).
Against that comes the normal paralleling considerations - ie, should not be left paralleled when not in use; take out any faulty battery; etc.... IE - matched batteries with symmetric connections if permanently connected in parallel, and battery monitoring is essential (often for safety as well as battery life).


But otherwise, I presume you are symmetrically connecting the batteries even if not depicted as such in your -ve paths.
The only problem I see is if you switch one of your old batteries in parallel with a new one when not being charged (ie, especially when idle), but in such situations batteries never remain matched anyhow so it becomes the usual argument of degree. [I'm pretty sick of some of the persistent & moronic POVs on that issue!]