Yet another battery question...

[wannabeangler]

I recently purchased a 2004 Tracker 175 Pro175 with a Motorguide 46# thrust trolling motor.

The original trolling battery (a megatron SRM-27 / 600CCA / 750 MCA) was dead when I purchased it and for the interim period, I threw in a small Wal-Mart deep cycle battery (24DP-4 / 675 amps / 550 cold charging amps / 105 amp hours). The smaller wallie-world battery only lasts about 2.5-3 hours.

Naturally, I'd like to get a battery that will give me a LOT more run time, but here's the real question:

Later this summer, I plan on dropping in a Minn-kota 24-volt, autopilot trolling motor.

With that said, can (should) I go ahead and purchase two 12-volt batteries and run them parallel? That way I already have the batteries needed for a 24-volt system. And what are the pros/cons of doing that versus purchasing a single bigger 12-volt battery?

Thx

[Wayne P.]

A group 24 deep cycle battery is not anywhere near 100 Ahr. It is closer to 75 Ahr. A lot of the group 27 deep cycles are.

For the best cost/performance set up, choose a group 27 size deep cycle battery. If you fish long days, you may want a larger size for the Auto-Pilot model since you will be powering two motors.

[wannabeangler]

Thanks for the info. Will running two 27's parallel (positive-positive, negative-negative) increase the Ahr to the current 12-volt trolling battery?

[Wayne P.]

One of the 27 series will handle most trolling motor needs for a day's fishing unless you fish as much as I do (10+ hours). I wouldn't bother connecting them together and just have the other one as a back up to take care of a particually windy or high current day.

Do you have a separate qroup 24 marine starting battery also or don't have a gas outboard?

[Way2slow]

If you're going to be converting to a 24 volt system later in the year, it would be better to go ahead and buy both batteries and connect them in parallel as you mentioned.

When you upgrade to the 24 system, the batteries will need to be connect in series. Series batteries need to be the same type, size and age (have close to the same number of charge cycles on them (no more than 25 cycles difference)). If you buy one now, you would have to replace it again with two matching batteries when you upgrade, so save yourself that money and buy both now.

To answer your question, you will get a little over twice the run time with the two batteries in parallel than with just one battery. If one gives you 3 1/2 hours, two will give you a little over seven hours.

Remeber though, when you go to a larger 24 volt motor, you may be back in the same situation running the group 24's.  Typically, group 24's are no larger than 75 - 80 Ah, group 27's are approx 105 and 30/31's 110 - 130.   

[wannabeangler]

Thanks for the info. And to clarify, if I were to run two 27's to a 12-volt trolling motor, then I would need to install a switch between the two batteries ... one that will allow me to draw off both simultaneously, right?

[TrackerG]

I have the same Motorguide bowmount 46# motor on my 17 and 1/2 ft aluminum. What I did was install another 27 series up front and put in a battery selector switch. That way I can run one battery til its low, then switch over and know how much battery I have left. The switch has settings for battery #1, #2, both or neither.

[NBR]

Two 12v batteries wired in parallel give you 12v with longer run time. You don't need a switch. Change the wireing to series and you get 24v. Series does reduce the time but you should have enough power for a full days fishing.

[Way2slow]

As mentioned, connected in parallel, you will be running off both batteries and they will both drain down and charge back as one big battery. I WOULD NOT install a switch to select which battery to run on and just run on one at a time. You will get noticably more run time drawing off both batteries at the same time.

Let me also clarify my statement about having the same problem of not enough run time when you go to a series circuit. If you go with the same trust 24 volt motor with the same two batteries in series, as you have with your 12V motor and the two batteries in parallel, you will get approx the same run time. Basically, both are going to burn about the same amount of watts.

What I was assuming is you will be going with a higher thrust 24V motor which will have a higher current draw, this will increase wattage usage and therefore, reduce runtime. That's why I said be carefull going with group 24 batteries, if you run you're TM long and hard, two group 24's on a much larger thrust 24V motor might come up short in the run time department.

[Fish Fast]

Not to hi-jack this thread (great thread by the way!), but If I have a single bank charger on my current 12 volt trolling motor ( with one battery ), and I decide to add a second battery with a paralell connection, do I need to get a dual bank charger or will the single bank charger charge both batteries, just as effectively as it did one, since they are both interconnected?

[Way2slow]

The recommended charge rate of your deep cycle battery is 10% of it's rated amphour capacity.  If you have a group 27, 105 Ah battery, that would be a 10 amp charger.  If you put another like battery in parallel with it, that effectively makes it a 210 Ah battery, so to properly charge it, you would want a 20 amp charger. 

If you charge them with the same charger you have, it will take twice as long to charge the two as it did the one.  If your onboard is one of those undersized 5/6 amp chargers to start with, that's the same as saying it will now be a 2.5/3 charger.  That's no more than a trickle charge, and over time your batteries will become more and more stratified, which will eventually ruin the batteries.

[Fish Fast]

Thanks way2slow!  I will prob. upgrade to a 24 volt trolling system as I don't think my 12 volt 55# will have enough umffff! to keep my jigs vertical on the detroit river (walleye) in my crestliner 1850 fishhawk.  Had I known what I know now, I would have negotiated a bigger trolling motor when i bought the boat. 

I may try a second battery in-line if my current 55# can hold its own on the river.....just not sure how long it will run on 1 battery or if the 55# will be enough?!?

We shall see!