Battery disconnects have no value..
Some folks use a disconnect to prevent theft of the bus. Most disconnects are not rated for the intended load. I can not think of any reason for a disconnect.
If the batteries need to be disconnected , take off a cable. Taking off a cable presents an opportunity to check all the connections. The first reason for alternator failure is poor battery connections, poor starter connection, or lastly poor altenator connections. Adding some wheel bearing grease to the battery connections prevents most corrosion..... A fully charged battery measures 12.6 volts with a multimeter.. Frank