Mercury Optimax – Boat Battery Wiring

Hello Kevin,

I have a 17 foot fishing boat with a 2004 115 Mercury Optimax and a 2007 9.9 Mercury kicker. I only have a single cranking battery for both motors. Mercury 9.9 Kicker

I was told that my marine electrical setup should have two cranking batteries, one for each motor hooked up to a boat battery switch.

The guy said I could damage the computer in my Optimax if by accident one motor was started while another was running. Would the automatic smart boat battery switch (the one you designed for your sister marine electrical site) prevent that if each motor was hooked up to separate batteries with this switch? How detailed is the marine wiring for this switch?

I really like the idea of this switch. My old boat had a Perko battery switch and I always forgot to switch it back and forth.



Hi Corey,

Your system is very common and I have not heard of people damaging computers in this manner. I have, however, heard of people damaging computers by turning the battery switch to the OFF position while the engine is running.

With our smart battery switch system, when either battery is above 13.7 volts, the batteries are connected together. When it drops below 12.8 volts, the switch opens and the batteries are not connected.

If you had your kicker connected one battery and your main connected to the second battery, while charging, the batteries are connected together and they would not be isolated to prevent the situation that you are describing.

The connection is fairly simple and we supply all of the boat battery wiring required with the Smart VSR Battery Switch System.

Please let me know if you have any questions,