Choose Blue Sea's 5511e Battery Switch if you have two separate (isolated) batteries that each have their own dedicated loads, and you want to switch them both on or off at the same time, with just a single switch.

This switch takes the place of two separate On/Off battery switches for example, if you have a dedicated starting battery wired to your engine, and a separate dedicated house battery wired to your circuit breaker panel.

However, this switch also has a "Combine Batteries" position which connects both batteries to all loads for emergency situations where you need the power of both batteries for use with either load. Typically you would use this function for emergency engine starting if your starter battery is low.
The 5511e Battery Switch can handle loads of up to 350 Amperes.

Isolates Start and House circuits, and combines both battery banks for emergency starting
Ignition protected - safe for installation aboard gasoline powered boats
Make-before-break contact design allows combining batteries without power interruption
Case design allows surface or rear panel mounting
Tactile indicator convery knob position by feel
Tin-plated 3/8-16 (M10) copper studs provide maximum conductivity and corrosion resistance
7/8" (22mm) stud length to accept multiple cable terminals
One-piece construction to reduce risk of overheating
Case design llows surface mounting or rear panel mounting
Accepts up to 4/0 AWG (95mm) battery cables