2 Dual Purpose Marine Batteries

[Supersportster]

I just recently purchased my first boat. 17 aluminum sylvan boat.

It came with two fairly new AC Delco, dual purpose marine batteries, that are hooked up to a switch which has position 1,2, and both.

The batteries are located at the back of the boat.

What I want to do, unless you guys with knowledge and exprience tell me otherwise, is to get two true deep cycle batteries, and one starter battery.

I have dead space at the front of the boat, which i could install the two deep cycle batteries, in parlell, with a little customization. Question one, will the added distance from the motor have an effect on battery usage or charging?

Question 2: Do I simply just put the starting battery to terminal one, and the two dual purpose batteries in paralell on termial two on the switch?

Thanks, let me know if it sounds like the right way to do it, or any better suggestions?

 

[Silvertip]

Re: 2 Dual Purpose Marine Batteries

Nice thought but there are two issues. A ground cable must be run from the parallel set of batteries to the negative terminal on the starting battery because the engine could not start nor would those batteries charge in either the BOTH or BAT 2 position. The second issue, is that your engine probably doesn't have enough alternator capacity to keep the starting battery and one dual purpose charged much less three batteries. You are better off installing an on-board charger with three outputs. You plug into shore power at the dock to keep those batteries charged. Just because the engine can charge a single battery, does not mean it has the capacity to charge three of them -- two of which would very likely be deeply discharged from the trolling motor. You would need to run wide open for hours to top off those batteries.

 

[Supersportster]

Re: 2 Dual Purpose Marine Batteries

Yea I assumed that I would have to top up the deep cycles by plugging into an electical output on shore.

If I ran a ground from the deep cycles to the starting battery, do you think the starting battery would keep charged up enough?

Or should I just keep the two dual purpose batteries i have, and get a good deep cycle battery and wire it up to my trolling motor, and keep it charged from shore?

 

[Silvertip]

Re: 2 Dual Purpose Marine Batteries

It depends on how you use the switch. If you run it constantly on BOTH you are essentially sharing whatever output the alternator has at that speed with three batteries. If you run on BAT 1 only BAT 1 gets a charge. If running on BAT 2 only the two dual purpose get charged. The start battery typically doesn't get deeply discharged so I wouldn't worry about running it down but as I mentioned -- it depends on how you use the switch. I would put the selector on BAT 1, start the engine, switch to BOTH and run to your destination. Switch to BAT 2 and do your thing. When ready to depart that spot you can do any of several things. 1) switch back to BAT 1 to start the engine then switch to both or BAT 2 when you leave. 2) switch to BOTH, start the engine and then leave. 3) Switch to BOTH, start the engine, then switch to BAT 2 and leave. Remember, BAT 1 was charged when you reached your destination so there is no need to be on BAT 1 for the return trip. On BAT 2 all of the alternator output would go the dual purpose batteries. Just so you know, you NEVER switch to OFF with the engine running.