pay close attention to the quality of your wiring installation, and fuse any positive wire as close to the terminal as possible. the second batt will be fused to the first batt and fused to the amp(s).
don't for get the big 3 upgrade, 1/0 wire all around.
yes already have the big-3 one thing I like to note ,on that 2-battery no-isolator diagram, it showed both batteries tied into a multi-fuse holder...this kinda throwed me becuase I never seen a fuse-holder like that without a neg side(input).