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Old 08-15-2013, 06:08 PM
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BAMBAM BAMBAM is offline
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Default Bad onboard charger... or what?

Here is my situation:
I have a 3 bank onboard battery charger. Batteries only a couple of years old.
When I plug in the charger, I read that my cranking battery is "green" and my trolling batteries need some juice... so I leave it plugged in. In morning, all indicator lights on charger are "green", or indicating fully charged. I go to start the engine, and nothing... no horn, cannot raise/lower engine, just dead. I put a 12 volt test light on battery and it says dead...but trolling motors all light up the test light, so I figure I have a dead battery and replace it.
New battery lights up test light, and when I put it in the boat, boat starts great and the charger shows that it is "green" (fully charged)

Question 1: If cranking battery was dead, why was charger indicating full charge?

Then, for giggles, I take old battery and put a stand alone battery charger on it...and it takes the charge, and when I put a test light on this old re-charged battery, it lights up test light. Now I am thinking that maybe I bought a new battery when really, I have a charger problem, and not a battery problem.

Question 2: How can I test the charger to see if in fact it is putting out a charge on my cranking battery? I am not an electrical engineer...so complicated answers with lots of testing equipment is not an option.

I have to figure out if I need to buy a new charger or not...


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Old 08-15-2013, 07:33 PM
fireboat fireboat is offline
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Default battery

I had the same problem yesterday. Green light on charger, reads 12.8 on the tester, won't turn over the motor. I took the battery to the shop for a "load test". Battery was dead. A load test at a battery shop is the only true way to determine if it's good or bad. Good luck.
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Old 08-16-2013, 05:00 AM
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Hawker Hawker is offline
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In order to find out if your charger is actually working or not you'll need a volt meter instead of a test light. Before plugging in charger, check voltage on battery in question. It should read somewhere in the vicinity of 12.2 - 12.8 volts. Now, plug in charger, and if charger is working properly, voltage should read (at the battery in question) somewhere in the vicinity of 13.8 - 14.2 volts. If you see no voltage increase from prior to plugging in charger to plugging in charger in all likelihood that bank of the charger is bad.
Steve "Hawker" King

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Old 08-16-2013, 06:10 AM
Hot Runr Guy Hot Runr Guy is offline
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If the use of a voltmeter scares you, pick up a simple digital unit that fits your cigarette lighter, and take note of the readouts. Like Hawker mentioned, there will be 1 reading for a no-running, not plugged in situation, a higher reading when the charger is plugged in, and a high reading when the outboard is running, and the alternator is charging the starting battery.


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Old 08-23-2013, 03:22 PM
Bill Krejca Bill Krejca is offline
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A few years ago I had a similar problem, turned out the inline fuse to that battery was burned, light showed fully charged.

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Old 08-23-2013, 04:56 PM
REW REW is online now
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Buy one of these:


After taking the batteries off charge, put the load tester - individually on each battery.

This tester puts 125 amp load on the battery and you should be able to maintain your 12.6 for a bit with that load on the battery.

Be safe
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battery , charger

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