This boat came into the shop with only a single battery but two ON/OFF switches. As we dug into the project, it seemed that this boat did at one time, have a 2nd battery. Somewhere along the line, it was consolidated to a single battery, which happen to be a deep cycle. Even then, the twin ON/OFF switch was a strange configuration, even back in 07. Dual bank switches are not new by any means.
We removed the old twin switches and installed a new Blue Sea 1/2/BOTH/OFF switch. Removed some of the extra, unneeded cabling. Relocated ALL the B+ load supplies to the switch output. Built new 1/0ga ground link cable between the banks and a new 1/0 B+ supply from the battery to the switch. New group 24 box and Interstate marine cranking battery.
One main switch turns the boat off when out of use. Operator can decide which bank to draw from, whether cruising or at anchor. One bank can always be kept isolated in reserve and both banks can be charged while the engine is running.