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I think at least one of my three trolling motor batteries is bad...what's the best way to test this?

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Use a digital volt meter. A fully charged 12v should read ~12.7 volts. Anything less is a potential problem.

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Thanks - my lowest battery is 12.95v

...but I'm running out of power on a long day on the water.

Trolling motor is an Ulterra 112 lb. thrust 36 volt.

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When you tested the batteries, did you disconnect the wires going to the other two batteries first?   Did you test at the end of the day before you plugged in your charger or right after you finished charging?

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I did a quick test this AM before I headed to work.  Batteries have been on the charger for 5 days and a night.

All three batteries were still connected in series.

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It is inconvenient I know but the best way to test them is by disconnecting the wires and using a battery load tester like this one.  The batteries must be isolated so the wiring must be disconnected.  It puts an electrical load on the battery which can tell you if a cell is going bad.  It only cost $22.00 from Harbor Freight.  Otherwise pull the batteries and go to Battery Warehouse or Auto Zone they will test it with essentially the same tester.  Now for the bad news.  If there is a bad cell in one they should all be replaced. These batteries should all charge to the same level and since they are hooked up to the same load they should all discharge at the same rate.  If one is bad I would replace all three with the same exact batteries at the same time 

Cen-Tech 61747 100 Amp  6/12V Battery Load Tester

Cen-Tech.gif
 
 
Cen-Tech - Item#61747

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Thanks - there's a Harbor freight store in Eau Claire...I'll see if I can get down there over lunch today.

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Give them a call first make sure they have one in stock. They carry several brands.

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Thanks - I appreciate the help...this is one of a few things I haven't tried before.

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You have one of the best load testers there is hanging off the front of the boat.  I'll bet you had a hellava time finding a 36V or any TM that size.  I guess that was a pocket model you can just keep in your tackle box. 

Just take your DVM with you when you have someone else going.   Or, just rig up a long test cable with a couple alligator clips so you can run the TM and check the battery voltage too.

Don't pay any attention to what the battery voltage is when you first disconnect the charger.  That's all surface charge and is meaningless.  Run the TM on max for about five minutes to knock off any surface charge, then take a voltage reading on each battery while the TM is still running on max.  All three should have about the same voltage and it still should be fairly high. 

After a couple of hours fishing and running the TM, check them again while it's running.  All three still should have close to the same voltage. 

At the end of the day, just before loading, make another quick check with the voltmeter and the TM running.  If any battery is much lower than the others, then it's time for a new set.  If all three batteries still have about the same voltage, they might being going out, but at least they are dying gracefully.

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Thanks for all the ideas and help.

Way2slow...great idea to test while running the trolling motor...but my batteries are in a compartment under my rod locker - not accessible while I'm fishing.

I bought a load tester, batteries test well into the green when fresh off the charger, and at roughly the same voltage as above (lowest @12.95, highest at 13.10).

Picture of what the read out is similar to - my needle was just to the left of where it is shown in this picture.

maxresdefault.jpg

Went out fishing, about 4 1/2 hours - I'm on the trolling motor a fair amount at about 20% - 30%, with some brief pops up to 40% or 50% and made one extended run (about 3 minutes) at full power.

Checked everything again when I got home, batteries were still right around 12 volts on the digital volt meter, but at around 10 - 10 1/2 volts on the load tester.

Batteries are Interstate 27 SRM if that helps.  Specs for the batteries:

http://www.interstatebatteries.com/p/srm-27-volkswagen-eurovan-1996-31-l5-2-4l?dsNav=N~21-2147384903

Product ID: SRM-27
Cranking Amps: 750
Cold Cranking Amps: 600
Voltage: 12
Termination: Common Code M
Weight (lbs): 50.3
Width (in): 6.75
Length (in): 12.75
Height (in): 9.50
ReserveCapacity-25: 160.00
WET/DRY: W

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I don't believe testing a battery when it's fresh off the charger will give you an accurate reading of the batteries health(as Way2Slow said). Charging them up and letting them sit off the charger without anything connected for a day or so before testing will give you a better idea of their status. As I'm sure you know, your batteries will only run as well as it's weakest one in the series. It sounds like you have one that is depleting quickly /w a bad cell/leak. Personally, I would replace all three batteries at once regardless /w ones that have the same stamp date even if just 1 was bad. 

What Way2Slow is asking you to do doesn't need to be done on the water.  You can do that at your house. You could also  take your fully charged batteries and attach the trolling motor individually to each battery one at a time and run it on max for 5-10 minutes. Disconnect the 36v series at the batteries and hook the positive/negative up to a single battery. Run it for 5-10 minutes on high and then take the a voltage reading. Do this to each battery. I would think they should all have the same voltage after being run. If one is lower, you found the problem child.  I think that would work at least...just make sure you run each battery individually on the TM for the same amount of time. 

Also make sure your connections are clean and free of any corrosion. Clean them. I'm not a fan of wingnuts either but make sure everything is tight. Loose, dirty connections can make you loser power. 

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iabass8, Thanks for the ideas.  I check (and clean as needed) the connections every spring, and they all looked good when I tested the batteries.

Unfortunately, I can't deploy the Ulterra while the boat is on my trailer, it runs into the winch on my trailer.  This is the only thing I liked better about the Terrova...

My thoughts at this point as that, as Way2slow said, the batteries are dying gracefully and I should replace them.

What I was trying to make sure of was that  it was a battery issue and not one with the trolling motor so that I didn't spend several hundred dollars on new batteries and find out it didn't make any difference.

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You do know they make a monitor you can install at the bow, that will let you monitor them from there.  I've  run a Curtis BDI on the bow for the last 15 years,   The Curtis would hit you pretty hard in the pocket book but BPS and places used to sell a panel that had a meter and switch so you could switch to each battery and check each individual battery, and they were not very expensive.

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It's been so long, I don't remember the model I installed, but it looks like this one http://www.ebay.com/itm/Curtis-Instruments-900R36BN-900R-36V-Battery-Fuel-Gage-for-Electric-Vehicles-/271870353388

Now, it's not as simple as just sticking it in.  I installed a small relay connected to the boats main power switch.  That way, you could turn the BDI or BSOC as they call them now, off and not have to worry about having to remember to turn it on and off from the front.  If not, it will stay one all the time.

I also like the Curtis because it does not fluctuate when you are running the TM.  I has a time lag to change voltage readings

I've run them two ways.  I've run a 12V one with a switch so I could check each individual battery and I've run the 24V/36 volt and just monitor the full voltage.  The one I'm running now, is a straight 24V, since that's the system I have.  Back when I got the things for free, I got a 12V, 24V, 36V and a 48V, just to make sure I covered all basis, but now I wouldn't be surprised if high voltage TM don't start showing up in something like 72 volt or higher.  I figure they will come up with someway to keep someone from electrocuting themselves with their TM one day.  When you get up that high, it can hurt you.

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Thanks - looks like that 900R will do what we're talking about.  I'll either put one in when I replace the batteries or at the end of the season when I put the boat away for the year.

I might add two 12 volt version for the starting and electronics batteries.

Thanks for the help!

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One on cranking battery is usually not needed.  Just about all good, LCD sonars will monitor battery voltage, and those are usually connected to the cranking battery.  So, unless you are still running a flasher, or off the TM batteries, you should have the cranking battery covered.

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I have a battery dedicated to my big motor, everything else runs off another battery.

I had an incident last year where a short in the charging cable for my Terrova remote killed the starting battery...since then, redundancy has ruled and anything not dedicated to to the main motor is separate...can't afford to be out in the middle of LOTW with a dead staring battery...

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I noticed you said you have a dedicated cranking battery and everything else is run off another battery. You aren't running your electronics/pumps/aerators/ etc off one of your TM batteries are you? You shouldn't have anything connected to your TM series except your TM itself. That's asking for battery failure. I bought the biggest, baddest AGM cranking battery /w the most reserve I could find and have never had a cranking battery issue since and everything except my TM is run off that one battery. You should be set up the same. 

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1 minute ago, iabass8 said:

I noticed you said you have a dedicated cranking battery and everything else is run off another battery. You aren't running your electronics/pumps/aerators/ etc off one of your TM batteries are you? You shouldn't have anything connected to your TM series except your TM itself. That's asking for battery failure. 

Nope.

1 battery for main motor.

1 battery for electronics, lights, everything else (except big motor).

3 batteries (completely isolated, separate system) for trolling motor.

...I'm kind of a nut about this stuff...

 

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16 minutes ago, Further North said:

Nope.

1 battery for main motor.

1 battery for electronics, lights, everything else (except big motor).

3 batteries (completely isolated, separate system) for trolling motor.

...I'm kind of a nut about this stuff...

 

You and me both. I've always been tempted to run a separate battery just for pumps and electronics as I have room for more batteries. Peace of mind kind of thing but I haven't had to...yet

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Doing that, I would run the second battery connected to the cranking battery through an Isolator.  That way the motor can help keep the second battery running the electronics, pumps etc. charged, but it can not discharge the cranking battery.

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Also note, make sure you are using a digital 3 stage charger with a separate bank for each battery, or charge each battery individually. Nothing will kill a deep cycle battery, especially if it's agm, faster than an older constant level battery charger.

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25 minutes ago, bmcphoto said:

Also note, make sure you are using a digital 3 stage charger with a separate bank for each battery, or charge each battery individually. Nothing will kill a deep cycle battery, especially if it's agm, faster than an older constant level battery charger.

I run a 4 bank Minn Kota 440D for the starting battery and the three trolling motor batteries.

I installed a 5th battery and charger this spring - an Interstate 24M and a Minn Kota MK 110 PC  - to separate out the electronics.

There are other brands of chargers that work just as well...but what I've got gets the job done and provides redundancy where I want it.

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