Bad onboard charger... or what?

[BAMBAM]

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...

Thanks!

BAM

[fireboat]

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.

[Hawker]

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.

[Hot Runr Guy]

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.

http://www.ebay.com/itm/12V-24V-Digi...753769&vxp=mtr

HRG

[Bill Krejca]

A few years ago I had a similar problem, turned out the inline fuse to that battery was burned, light showed fully charged.

Bill

[REW]

Buy one of these:

http://www.northerntool.com/shop/too...6099_200456099

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