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Old 06-07-2014, 14:19   #1
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Did I kill my batteries?

In another thread I explore why my electric winches are slowing down and the unanimous advice is that I have a battery problem. Here: Electric winches slowing down - problem lurking?. Basically my winches slow down quite noticeably while under constant load (about 60 seconds of hoisting my butt up the mast)

I have six 8GGC2 6 volt Gel batteries arranged in three pairs for 12 volts and approx 540 aH. They were new in May of last year and worked fine until I laid up the boat in November with the batteries fully charged. The winter was extra frigid so I'm suspicious the batteries froze. In April the volts checked at approx 3.5 for the bank. Not good. I had to use an automotive charger to bring them up enough to let my Trace charger/inverter kick in and take over. They've been on shore power ever since, except while sailing of course, and I've confirmed the charger setting are correct per the manual.

They seem to lose their charge faster than they used to, and don't hold as high a charge. I did some testing a few days ago hoping this data would help me get help from the experts here.

With the charger turned on my volt meter tells me I have 13.4 volts.
Turn off charger and wait a few minutes (no load on) and the volt meter settles at 13.0 volts.

Next I disconnected all the batteries and took a voltage reading of each one individually. They I reconnected them, turned on enough equipment to see a 10 amp drain on the bank, and left it that way for 1 hour. Then I removed the load, disconnected all the batts again and took another reading. Below are the before/after readings of my six batts (in Port, Center, Stbd pairs):

P1: 6.53/6.38
P2: 6.51/6.37
C1: 6.51/6.38
C2: 6.49/6.37
S1: 6.49/6.38
S2: 6.48/6.36

Full bank: 13.00/12.6

I also have a new Balmore SmartGauge battery monitor that has seen several use cycles now and should be calibrated. It tells me my State of Charge is 84% before and 81% after my test. I don't know yet to believe this. It has never gone above 85%, which is disturbing.

Are my one-year-old batteries damaged?

All advice appreciated.


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Old 06-07-2014, 21:56   #2
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Re: Did I kill my batteries?

I think I see one problem. You have the + and - leads coming off the same end of the bank. The batteries at the far end of the bank are not getting charged properly. Check out the Trojan web site and find their recommendations for how to wire up a battery bank.

Also you should ensure that you are charging your batteries in accordance to the manufacturer specifications.

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Old 06-07-2014, 22:26   #3
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Re: Did I kill my batteries?

if your batteries were down to 3.5v and left like that for a while (days / weeks) they are probably damaged and / or weakened.

you should have left a float charger on over the winter.

the only way to test them is a 20 hour test. then you will know the real capacity left of you batteries. look it up.
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Old 06-07-2014, 23:17   #4
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You need to test the batteries voltage with a high load on them. I just replaced 8 year old batteries. after sitting overnight voltage was fine can't remember exactly but close to 12.6 and I have a fridge and fans running 24 7. But they would not start my engine. Edit I just read the post above mine and agree that's the way to find out what capacity you have left. Quick and dirty or scientific the choice is yours
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Old 06-07-2014, 23:53   #5
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Re: Did I kill my batteries?

I agree with DeepFrz. This is a common fault. Also, make sure you are not loosing electrolyte. A frozen batt can split the case....

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