Need a boat battery guru

[Eric Hug]

Ok, I need to know how long I can fish without starting the big motor to charge my battery. I have a cx18ss powered by an ultrex 80. This does fine for as long as I have ever fished never had a problem. I have a 150 Merc four stroke and 2 graphs hooked to the starting battery. The other day I was fishing and found a good hole and fished for quite some time. I have my mega 360, helix 9 at the bow, and helix 8 at the graph running for this entire time. I go to start the big battery and leave and it won't crank. I get home on the ultrex and start looking at the batteries. The boat is only a year old and haven't paid attention to what the dealer put in. Come to find out I'm running a deka group 27 for my graphs and big engine. No wonder it didn't start. So I go to AutoZone, spend nearly 500 dollars on a group 31 odyssey performance. Figure I'm set. Go out today and while the battery still did have enough to turn it over, I got a warning to check the battery voltage.  All this just to ask... How long should I be able to sit and fish with those two graphs on and the mega 360?

[TnRiver46]

I always crank my engine at least every 3 hours or so , just to keep her juiced. I doubt there’s an exact time but I just do it for piece of mind. I did accidentally leave my graph on in my carport all night once and my battery was still reading 12.4 v 

[Tennessee Boy]

I ran a Solix 9,  a Solix 15,  360, Mega Live,  a network switch,  a heading sensor, and a GPS puck on my cranking battery which is a X2 Power group 27.  I never worried about keeping the battery charged and I never had a problem starting the motor.  Last year I added a battery just for my electronics because I was having various problems with the electronics caused by the voltage drop when I cranked the motor.   Solix units are notorious for their voltage sensitivity.  
 

My guess is you’re getting a warning on your fish finder when you crank the motor.   The voltage is going to drop a lot when you start the motor and that might cause some problems with your electronics.  I wouldn’t expect it to cause any damage.  
 

So to answer your question,  I would guess you can go several hours without cracking the motor but expect some warning messages and possibly some other issues when you crank the motor.

[WRB]

You bought a automotive alkaline battery not a deep cycle marine AGM battery.

You can use the group 31 For a house battery and use a good AGM group 27 for a cranking battery.

Or return the auto Odyssey for a Deep cycle marine Odyssey battery.

Tom

[casts_by_fly]

A helix 9, 8, and 360 is going to draw about 6amps on full power. A group 27 is going to be around 70 Ah. You’ll take the battery from full to half in about 7 hours. The question becomes how many cranking amps will your battery deliver at half charge. also, how full was the battery when you started?  Did you charge it fully before starting the day or are you relying on the motor?

 

best course would be to keep the group 31 as a house battery and pick up a group 24 cranking battery. 

[Eric Hug]

9 hours ago, TnRiver46 said:

I always crank my engine at least every 3 hours or so , just to keep her juiced.

Is this what I should expect?

 

7 hours ago, WRB said:

You bought a automotive alkaline battery not a deep cycle marine AGM battery.

You can use the group 31 For a house battery and use a good AGM group 27 for a cranking battery.

Or return the auto Odyssey for a Deep cycle marine Odyssey battery.

Tom

This is the battery I purchased it is not an automotive battery.

 

 

Odyssey Battery Performance 31M925 Group Size 31 Dual Purpose Deep Cycle Marine Battery

 

 

6 hours ago, casts_by_fly said:

A helix 9, 8, and 360 is going to draw about 6amps on full power. A group 27 is going to be around 70 Ah. You’ll take the battery from full to half in about 7 hours. The question becomes how many cranking amps will your battery deliver at half charge. also, how full was the battery when you started?  Did you charge it fully before starting the day or are you relying on the motor?

 

best course would be to keep the group 31 as a house battery and pick up a group 24 cranking battery. 

Overlooked this answer sorry. The battery was charged fully both times. By a dual pro trio 15 amp per bank. when I brought it back to the house it charged very quickly. So the battery I mentioned above, how many cranking amps will it have at half charge? I was fishing for around 3 hours without starting the engine. The warning came from my boat not my fish finder. I'm beginning to wonder if something is wired wrong or if my expectations are too high...

[Jig Man]

Today’s electronics draw a lot of juice.  I experienced the same problem that you described when I had Lowrance units.  I now have Humminbird units and the problem did not go away.  I tried several different cranking batteries and it still existed.  I spent several hundred dollars at boat shops trying to get to the bottom of this issue.  I wound up getting a house battery for the electronics.  It has been working fine for three years.

[TnRiver46]

1 hour ago, Eric Hug said:

Is this what I should expect?

 

This is the battery I purchased it is not an automotive battery.

 

 

Odyssey Battery Performance 31M925 Group Size 31 Dual Purpose Deep Cycle Marine Battery

 

 

Overlooked this answer sorry. The battery was charged fully both times. By a dual pro trio 15 amp per bank. when I brought it back to the house it charged very quickly. So the battery I mentioned above, how many cranking amps will it have at half charge? I was fishing for around 3 hours without starting the engine. The warning came from my boat not my fish finder. I'm beginning to wonder if something is wired wrong or if my expectations are too high...

I don’t know about expect , I just crank the motor for piece (peace?) of mind. If I’m on trolling motor for hours it’s in the back of my mind. Especially after dark with running lights on 

[casts_by_fly]

3 hours ago, Eric Hug said:

Overlooked this answer sorry. The battery was charged fully both times. By a dual pro trio 15 amp per bank. when I brought it back to the house it charged very quickly. So the battery I mentioned above, how many cranking amps will it have at half charge? I was fishing for around 3 hours without starting the engine. The warning came from my boat not my fish finder. I'm beginning to wonder if something is wired wrong or if my expectations are too high...

hard to estimate cca on a run down battery but a couple online charts are showing about 100 cca per 10 ah. That’s for capacity, not run down, but using that estimate you’d have dropped about 20 ah in 3 hours which would be about 200 cca. If that was the deka group 27 cranking battery, you started with 650 cca. That would have put you around 450 cranking amps. 
 

however, the drop in cca with ah estimate would be based on the battery at full charge voltage. Your voltage would have been lower too so I’m guessing it might be even lower than that. Either way, the group 27 clearly wasn’t enough. The oddesy you bought is 925, so you have and extra 300 cca to work with. 
 

since you already own both, if you can fit it I would keep the 27 as the cranking battery only and use the 31 as the house battery. 
 

 

 

[GaryH]

I run 4 Birds, mega 360, mega live, PP with no issues but to be safe I installed an Ionic emergency start on the cranking battery. It’s $129 and is attached right to the battery. If you run down your battery and it won’t start you either push the button on the emergency start or turn it on with your cell phone. 

[WRB]

Marine deep cycle batteries you should be in good shape with the batteries you have.

Norco had a good jump start battery device and makes water proof onboard chargers at a decent price.

Good fishing,

Tom

[WIGuide]

Not an expert, but the 150 4 strokes are strongly recommended to run a battery with 975 CCA or higher. If going with something smaller than that, I'd definitely be going out with some sort of jump switch, cables, or box to make sure you aren't stuck out there.