Smart Switch Simplified

Hi Kevin,

I have a charging system on my dual boat battery wiring setup that only charges the battery when the boat is plugged in to shore power.

I have an Evinrude 120 outboard single engine.

How do your boat battery switches that have a voltage sensitive relay keep the batteries charged when underway as well as at the dock? BEP Voltage Sensitive Relay

Do I hook up the charging system to the VSR positive terminals to let it switch back and forth or just to the switch as in the diagram?

Thank you for your time.


An automatic smart switch is a nice addition to any dual battery boat wiring – and a must have for trolling systems.

Simply, the VSR connects between the two position battery posts through the battery switch. When the engine is running, the engine battery voltage goes up above 13.7 volts, the VSR engages and allows the alternator to charge both batteries.

If you would like to have both batteries charged by a single output battery charger, simply put the battery switch in the ON position and connect the charger to one of the batteries. When that battery hits 13.7 volts, the VSR will engage and allow both batteries to charge.

Hope this helps,


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