Dual purpose marine batteries?

I do a lot of night fishing and am always running into issues with my starting battery dying. Last year I purchased a brand new cranking battery as well. I leave my boat lights on anytime I am on the water at night and I know this drains the battery. I also like to leave my GPS unit on to make sure I’m not drifting off location. Ive never used the ‘dual purpose’ batteries because I have always thought I would be better off purchasing a battery that was more application specific. Has anyone used dual purpose? Does anyone have suggestions? Would it help to run multiple starting batteries in series?

I had 3 starting/deep cycle batteries in my old boat and they worked for years and I never had any issues. I had one for starting/electronics and the other 2 for a 12v, then 24v trolling motor. They were only size 24 and had long run time until they were about 4 years old. If your battery is dying after one night of fishing, I’d say your battery needs to be replaced. Get at least a size 27, or 29 if you can if you want longer run time.

I had the same problem. Running lights are tough on the battery and running around on Pool 2 wasn’t going to charge it back up again. My solution? I put a dual bank smart charger in my boat. That way I know the battery gets charged up and is ready to go.

SR

Put the BIGGEST battery you can fit in your boat. Hopefully you can get a group 29 in it. Changing out your lights to LED’s should cut down on battery drain also.

A deep cycle battery will do what you are asking. Just make sure it has enough MCA for your motor. I run group 31 for starting/electronics batteries. I would start there and go to a group 29 if a 31 don’t fit

puddlepounder wrote:

A deep cycle battery will do what you are asking. Just make sure it has enough MCA for your motor. I run group 31 for starting/electronics batteries. I would start there and go to a group 29 if a 31 don’t fit

X2. This one from Sam’s, made by East Penn/Deka, is a pretty good value.

http://www.samsclub.com/sams/duracell-marine-battery-group-size-29hm/prod3590216.ip?navAction=push

HRG

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Deep cycle batteries would work for “cranking” scenarios but it isn’t the best application due to how the battery is designed. Deep cycle batteries as the name entails depend on long run times and deep discharge cycles followed by extended recharge cycles. They do not handle “quick burst” discharges (like what’s done when you crank your motor) very well at all. This is where a dual purpose battery comes in with a better application.
I have a dual purpose battery (size 29) at my cranking location which is my electronics, lights, livewell, etc. Deep cycles for my trolling motor.
No complaints at all in many years of running the dual purpose at the cranking location. Prior to that it was a “starting” battery and it didn’t last long. I always had issues with the GPS units turning off, etc.

I keep my starting battery for starting the engine only and I have everything else running on a different battery. That way I can always have power to start the engine. The river at night is no place to get stranded. Also led lights are a great idea to keep the lights on longer.

CaptainMusky wrote:

Deep cycle batteries would work for “cranking” scenarios but it isn’t the best application due to how the battery is designed. Deep cycle batteries as the name entails depend on long run times and deep discharge cycles followed by extended recharge cycles. They do not handle “quick burst” discharges (like what’s done when you crank your motor) very well at all. This is where a dual purpose battery comes in with a better application.
I have a dual purpose battery (size 29) at my cranking location which is my electronics, lights, livewell, etc. Deep cycles for my trolling motor.
No complaints at all in many years of running the dual purpose at the cranking location. Prior to that it was a “starting” battery and it didn’t last long. I always had issues with the GPS units turning off, etc.[/quote

99.999999% of a starting batteries life is running all of your accessories. The .1% is starting the motor. It takes about a 1 to 3 second burst of power to start a motor, your electronics are on all day/night, you do the math, what does the battery do more of? Starting or deep cycle service?
the issue with your GPS shutting down at start up is you have the GPS wired through a fuse box/boats wiring system. The GPS units should be hard wired directly to the battery with a fuse.

puddlepounder wrote:

99.999999% of a starting batteries life is running all of your accessories. The .1% is starting the motor. It takes about a 1 to 3 second burst of power to start a motor, your electronics are on all day/night, you do the math, what does the battery do more of? Starting or deep cycle service?
the issue with your GPS shutting down at start up is you have the GPS wired through a fuse box/boats wiring system. The GPS units should be hard wired directly to the battery with a fuse.

Agreed on what your battery does during its lifespan, my point is that a deep cycle is not designed to take large loads that a large outboard kicks out when trying to start — 50 amps in some cases. They are designed for long runs of low amperage and a deep discharge. This was comparing a “starting” battery with a “deep cycle” battery.
Dual purpose blends the two, but does handle the deep draws of cranking an outboard similar to how a cranking battery would.
BTW, my electronics haven’t been connected through the fuse box in years. I still had that issue when I had a cranking battery, but when I upgraded to a dual purpose (also larger size) the issue completely went away.
Like I said, a deep cycle will work in this application, but it most likely will have a shorter lifespan than a dual purpose for that application.

If you have a Humminbird hooked to that battery,
set the minimum voltage alarm
to warn you to start the engine and recharge the batteries.
I emailed Mercury and for my 90 hp 4 stroke,
they recommended 11.5 volts.

mxskeeter wrote:

Changing out your lights to LED’s should cut down on battery drain also.

X2 Your lights will draw much more than your locator and or GPS.

Great info, thanks for the help everyone. A little annoying that the new starting battery that I purchased last year doesn’t work for me. Any suggestions for LED boat lights? I am also putting some LED interior lights in my boat this year as well. I should be hooking these up to my starting battery as well, correct? I have a buddy that shames me for not running accessories to my trolling motor batteries.

Trolling motor batteries are just that, batteries dedicated to the trolling motor. If you are running a 24v or 36v system, powering a 12v system won’t work. Having a extra battery to run all accessories isn’t a good idea either, more weight, takes up more space, doesn’t charge when main motor is running to name a few. As long as your deep cycle battery has enough MCA to start your motor, you are golden. A deep cycle battery can do everything a starting or dual purpose battery can do, so it makes sense to have a battery that will run all of your accessories all day/night without any concerns than to have a starting or dual purpose battery and wonder if your motor will start.

A cranking battery works just fine. I have been running all my accessories and graphs off a single m24 size cranking battery for years. The batteries are designed different for specific reasons. This information is best to hear from a battery profesional. Throughout the years of rigging boats I have heard all sorts of smoke blown about why someone thinks it should be one way vs another. If the boat is properly rigged a cranker is all you need. All my graphs are hooked to my main power source panel. No need to run wires to a battery if your power source is correctly working. Most of the time people have a power draw somewhere. Running longer wires is not the answer.

doesn’t charge when main motor is running

Mine does.
I use a Minnkota mk2-dc to charge my TM batteries on the water.
Spot lock for a week up at Voyageurs without access to electricity every year.

Use a 31 agm battery or better an odessey. The agm will hold better charge then a standard lead acid. The odessey batteries are a better pure lead and will be even better.