For protection of sensitive electronics during starting, then Consider one of the three diagrams below. These are all essentially the same but shows slightly different connecting points. This protects the sensitive electronics from dropout voltages when the 4 way switch remains on battery 1 while cranking. Normal operation would be to simply leave the 4 way switch in position 1 all the time unless you need an emergency start from battery 2. Both sides will automatically receive charge.  Consider connecting a simple micro-switch or Remote Module to the BIC-95150B so you can manually combine batteries before switching.    This will reduce arcing and save wear on the heavy switch contacts. Just be sure to switch it open after moving the 4 way switch and before any cranking   Or simply leave the Remote switch not connected.

And, below is a fourth possibility where the only difference is where the Fuse Box / Power Distribution is connected.

Pros:  

• Optimized configuration for a single "two-bank switch" with sensitive electronics isolated from the starting circuit.
• Simple.    Minimal wiring needs.  
• External solenoids NOT required.  
• Two or more BIC's can be used in parallel to increase current handling capacity.
• Medium Cost.   (Unless you already own the switch.)
• Simple to understand, installation!  
• Simple automatic charging operation!    No need to leave the switch in the Both position for charging.   No hassle, worry free.
• Because the alternator is connected directly to Battery 1, you have the ability to switch positions on the 4 way switch while the engine is operating (even to OFF) without damage to the alternator.  
• Simple manual parallel combination via a remote micro-switch.    From a remote console, you can use very small wire running a long distance to switch the batteries in parallel!  
• The Hellroaring and BIC-95150B tends to limit inrush currents when switching when wired with the recommended size and length of wire.    No arcing to wear out the device!
• No diode voltage drop effect when ON!  
• Another option is to leave battery 2 with no loads connected and reserve it just for emergency starting.

Cons: (these may not all be cons)

• Off position of the 4 way switch disconnects only the starter and power distribution panel in the first three diagrams. The sensitive electronics are not affected. You may consider a single manual disconnect for the sensitive electronics if desired to have that ability as well. In the fourth diagram, you may desire another disconnect switch for your power distribution panel.

If you have any questions regarding your particular application, feel free to send an e-mail question to the contact link below.