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Old 07-06-2010, 18:20   #1
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Batteries and Charger

I have a 1991 hunter legend 35.5 (just bought). The boat has 3 house batteries and one start battery. It also came with a pro mariner 50 charger Not hooked-up. I hooked up one +positive lead to the starter battery, and the other + positive lead to the first battery in the group of house batteries. the only - negative lead i put on the start battery neg post (all batteries seem to be wired together. when i turn on the charger it seems to be charging but only to 9.20v however when the motor is running it shows 10.80 v. The volts in both cases drop when either motor or charger is turned off. Does this indicate that the batteries are going bad or that i have the charger hooked up wrong, or both. Any help would be appreciated or a suggested book(book for a dummy). Thank you.
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Old 07-06-2010, 18:42   #2
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Boat: Alden 50 in Narragansett Bay, RI
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It sounds like the charged is connected properly but you don't mention what the output of it is so it's not possible to determine if that is your problem. Check it first - always do the easy stuff first!

If it's okay, disconnect all batteries. Using a hydrometer, check each cell to verify the sp. gr. is close top what it should be and close to all the other cells. If not, get out the wallet...

In either case, it sounds like all the batteries are toast.
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Old 09-06-2010, 17:25   #3

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"when i turn on the charger it seems to be charging but only to 9.20v however when the motor is running it shows 10.80 v."
Voltage levels that low indicate either a dead battery or extensive corrosion on the wiring.
I'd suggest "divide and conquer". Buy a $20 multimeter at WalMart or Target, that's good enough to start with. Using the 20VDC scale, test the output of the battery charger, all by itself with no battery connected. Most will read 15-17VDC with nothing else connected. Get the manual for that charger, because some of the newer ones are too smart, and they won't charge a deeply discharged battery at all.(Because there is some danger of overheating and explosion.)

Once you know the charger is good, test each battery, See if any read above 12VDC. Try to charge one, and just one, at a time, and charge it directly with the other batteries not connected. This will tell you if one or more batteries are shot or if there is a wiring problem.

Use the hydrometer, and buy the big one (12" not 4") when you do. It will try to spit or drip battery acid, so wear old clothes and expect acid burns in them no matter how careful you are. I keep mine in a plastic case because no matter what you do with it, it either smashes or scatters acid drops unless it is cased up somehow.

All the terminals and cables should be clean--clean enough to eat off them. If not, clean them. If any of the cables are not tinned wire, and they show green crud at the ends? They need to be replaced.

That should give you a start on it. Four batteries at once is a lot to troubleshoot. Divide and conquer, one is enough to start on.
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