Looks pretty good at first glance, good circuit isolation and branch circuit protection, plus nice power and ground busses.
Can't tell in your drawing, but ... Make sure your master switch has a 'Combine' setting, else when your start battery goes flat, you won't be able to use your house battery to start the main motor. Also, you may want to consider using an automatic charge relay (ACR) - They generally will charge the lowest battery first, until a threshold is reached, then will combine the batteries and charge them both at the same time ... during charging, the lower battery gets most of the charge until they're equal. Good ACRs also have a low-voltage cut-off that prevents charging to that battery if it's a failed battery and the voltage is too low. All good stuff and works well with liquid acid batteries. I think Dan Boccia came up with a better solution for batteries that are best charged with a 'smart charger' that automatically runs the charging cycle from bulk through trickle charging to maximize the charge that the batteries take. Can't remember.
Blue Sea Add-a-Battery KitBrian
