View Full Version : Auto Battery in my Setup question

08-19-2005, 09:40 AM
New boater question... I have a 2 battery setup on my Indmar 351W. The main starting battery is a Red top Optima auto battery and the second battery is a Walmart Deepcycle marine dual purpose unit hooked up to a Perko selector switch.

I use the Optima as the starting/cruising battery and when anchored or stopped I use switch over to the Walmart deep cycle battery.

Is there anything incorrect about using this method?

I know the Optima is not deep cycle marine but it is always being the one charged, similar to a car situation so it should last just as long, should'nt it?

08-19-2005, 09:52 AM
I can't answer the question you asked - but while cruising - I always switch the perko to both batteries. When anchored - I switch to my deep cycle and "save" a starting battery in case the deep cycle runs too low.

08-19-2005, 10:01 AM
I believe the Optima should be ok as long as the cranking amps are appropriate for you motor which it probably is but you can check. A marine deep cycle is better suited but you donít need to go buy one just to replace it.

What you want to do is start your boat in position 1 (the Optima) and then while under way switch to position ALL which charges both batteries simultaneously. Once youíve stopped and you want to run accessories switch to position 2 to run off the deep cycle.

When you want to get under way again switch back to 1 to start youíre boat and repeat the above procedure. This will keep both batteries topped off and you should never have a dead starting battery. :D 8):D

Thatís my .02, hope it helps and thatís how I use the same setup.

Screaming Reels,


08-20-2005, 08:33 AM
Be sure and check with the mfg of the switch to see if you can switch while charging/underway.

08-20-2005, 10:11 AM
What Chetco is suggesting is to make sure that your switch is a "make before break" type of connection design. Most if not all newer battery switches are of this type. But I once blew out a voltage regulator and the diodes of an alternator back in the '80's by switching batteries while the engine was running.

The only limitation of automotive startup batteries in a boat is that the plates are not as thick as those found in deep cycle or combination batteries. So they are more susceptible to damage from vibration or hull pounding. However, if you battery is mounted in the stern it will probably hold up fine unless you run in very rough water.

08-20-2005, 09:07 PM
would an automotive battery work on a trolling motor under 40 lb thrust? how long would it last?

08-21-2005, 05:27 PM
It would be toast after a few full cycles. The plates get sulfated and the battery stops accepting a full charge. Deep cycle batteries are designed for just that purpose. They work fine as startup batteries as well. Since they cost more that startup batteries and don't deliver the same peak power (not really necessary in most cases), they are not used in cars. However, they are used as starting batteries for diesel engines with manifold heaters. I had a pair hold up for over 5 years in my Dodge Cummins.