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Old 06-26-2013, 10:26 AM   #1
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Battery bank @ 12.4 volts?

The 6 golf cart bank on our boat shows 12.4 volts on the Link and on a good meter after a couple of hours "at rest". It's a bear to access, so before I start removing the interconnect cables to isolate each battery, I'm wondering if a bad cell is the most likely cause??
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Old 06-26-2013, 10:43 AM   #2
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What do you mean "bad cell"???

From your description there is nothing wrong with your battery bank.

Bag your troubleshooting and enjoy your boat. 12.4 volts out of a 12 volt system is just fine!

Here's how lead acid batteries really work on boats.

Your charger will end up while on shore power "floating" your battery bank at somewhere between 13.1 and 13.5 volts. Opinions vary as to the best float voltage but anything in that range will work just fine.

Once you remove shore power the normal loads on your boat will draw current from your batteries. Boats all vary as to the actual loads, but even the smallest cruiser has at least a fridge on all the time.

Your battery voltage will go down and stabilize at 12.0 volts. It will stay at 12.0 volts give or take during much of the discharge cycle.

As the batteries are depleted they will eventually go down in voltage somewhat depending on how deeply you discharge them prior to re-charging.

There is a battery myth floating around here to read the "at rest" voltage of your bank to judge its health and or charge. While that method might be OK for a set of batteries with no load, it is not applicable to a marine house bank, bacause a house bank does not sit "at rest". Even if you removed all loads from your house bank the "at rest" voltage method is not all that good.
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Old 06-26-2013, 10:46 AM   #3
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Each cell generates 2.1 V, so doesn't sound like a dead cell.

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Old 06-26-2013, 11:00 AM   #4
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Originally Posted by ksanders View Post
What do you mean "bad cell"???

From your description there is nothing wrong with your battery bank.

Bag your troubleshooting and enjoy your boat. 12.4 volts out of a 12 volt system is just fine!

Here's how lead acid batteries really work on boats.

Your charger will end up while on shore power "floating" your battery bank at somewhere between 13.1 and 13.5 volts. Opinions vary as to the best float voltage but anything in that range will work just fine.

Once you remove shore power the normal loads on your boat will draw current from your batteries. Boats all vary as to the actual loads, but even the smallest cruiser has at least a fridge on all the time.

Your battery voltage will go down and stabilize at 12.0 volts. It will stay at 12.0 volts give or take during much of the discharge cycle.

As the batteries are depleted they will eventually go down in voltage somewhat depending on how deeply you discharge them prior to re-charging.

There is a battery myth floating around here to read the "at rest" voltage of your bank to judge its health and or charge. While that method might be OK for a set of batteries with no load, it is not applicable to a marine house bank, bacause a house bank does not sit "at rest". Even if you removed all loads from your house bank the "at rest" voltage method is not all that good.
Guess I thought there was an issue because the bank used to settle at 12.6 with everything off. The house bank has been in float mode on the three stage charger for a couple of weeks. I did have the big panel switch set on "off" before the "at rest" period, and the fridge was running on AC. For some reason I thought a weak cell in one of the six batteries might pull the overall voltage down. Guess not. Anyway, thanks...I'll not worry about it. Not a big deal at the marina anyway...just thinking ahead for an upcoming extended cruise.
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Old 06-26-2013, 11:51 AM   #5
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If you really want to test your battery bank, then just unplug your shore power cord, letting your boat discharge the battery bank just like you were on the hook.

I did just that yesterday. I called the harbor and had someone shut off my shore power breaker in the morning.

I monitored the voltage throughout the day, and it stayed at 12.0 volts +- 0.1 volt.

At the end of the day I called the harbor and asked them to turn back on my shore power.

I did not believe I had an issue, but I'd seen some voltage fluctuations on my alarm system so I thought it was a good idea to check. I know my boat draws something around 20 amps +- DC all the time so I know it was a good test.

Here's the cool thing...

I did it from home.
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Old 06-26-2013, 12:22 PM   #6
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Since you said getting to the batteries isn't that easy, so no load test or specific gravity readings, unplug from shore power and shut off all your DC loads. After several hours your batteries should be at ~12.65. If they are at 12.4, you need to access them unless your charger isn't working correctly. How's the water level?

How old are your batteries? If they are 5 years old, give or take, they could be just worn out or sulfated.
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Old 06-26-2013, 12:31 PM   #7
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Well, I don't agree with everything that has been said here. A true resting voltage which is what the OP has measured is a valid indicator of battery state of charge. If it was 12.6 and it is now 12.4 then something has changed for the worse.

But, not to belabor it, the simplest way to know the condition of your house batteries is to do a load test. Charge the batteries fully with the shorepower charger then turn it off. Then turn on enough lights or some other continuous load to pull enough current equal to about 1/20 of the battery bank capacity. You will need a clamp on DC ammeter for this.

Then let it sit for as long as it takes for the lights to dim and get down to 10 V or so. Amphour capacity equals average current times hours to discharge.

I have done this for gels and AGMs which can't be checked with a hydrometer and it works.

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Old 06-26-2013, 01:06 PM   #8
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Quote:
Originally Posted by skidgear View Post
The 6 golf cart bank on our boat shows 12.4 volts on the Link and on a good meter after a couple of hours "at rest". It's a bear to access, so before I start removing the interconnect cables to isolate each battery, I'm wondering if a bad cell is the most likely cause??
As 12.4 the battery is a 50% and less that 12.0 it dead and need replacing.

How old are the bateries.
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Old 06-26-2013, 02:14 PM   #9
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Should be around 12.6 (fully charged, no load) and you don't have to disconnect the 6v batts...just check across each batt's terminals and you should have about 6.3 on each one.
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Old 06-26-2013, 02:55 PM   #10
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Should be around 12.6 (fully charged, no load) and you don't have to disconnect the 6v batts...just check across each batt's terminals and you should have about 6.3 on each one.
Yes, of course. The electrolytes in my brain must be low. I'll shut everything down and check each of them. And then probably do as suggested and turn off the charger and do a long term load check.

The bank is on it's sixth summer...mostly in the slip and on the charger for four months. During the time in the storage building, they get charged roughly once per month. Equalized at Spring launch, mid summer, and before haul out in the Fall. Water levels always kept up. But in spite of light usage, they are getting old. Thanks for the info and advice.
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Old 06-26-2013, 04:04 PM   #11
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I'm going to be perfectly honest here...

I have been to two several day each battery maintenance schools for flooded lead acid batteries. As part of my profession I have maintained industrial flooded lead acid battery systems in Telephone Central Offices, Microwave sites, Ocean Fiber Landing Satations, and Power Substations for over 30 years.

I say this to give a little history, and perhaps some credance to what I'm going to say.


During all that time, several employers, many many systems, I have NEVER used a no load "at rest" method to determine battery system health. Never.

Most companies I've worked for used a battery discharge test, where we put the batteries on a load for a specific period of time, while measuring the per cell voltage, and intercell (strap) voltage drop, etc...

I do not dispute that some recreatiuonal battery users utilize a "no load" test, but thats not a testing methodology people that work on live industrial battery systems for a living generally use. At least not in the telecommunications, or power industries.

I could stand corrected though. In the last 100+ years of battery system maintenance history the nice folks at the phone company have learned allot about battery maintenance, but clearly not everything.
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Old 06-26-2013, 04:50 PM   #12
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Quote:
Originally Posted by ksanders View Post
I'm going to be perfectly honest here...

I have been to two several day each battery maintenance schools for flooded lead acid batteries. As part of my profession I have maintained industrial flooded lead acid battery systems in Telephone Central Offices, Microwave sites, Ocean Fiber Landing Satations, and Power Substations for over 30 years.

I say this to give a little history, and perhaps some credance to what I'm going to say.


During all that time, several employers, many many systems, I have NEVER used a no load "at rest" method to determine battery system health. Never.

Most companies I've worked for used a battery discharge test, where we put the batteries on a load for a specific period of time, while measuring the per cell voltage, and intercell (strap) voltage drop, etc...

I do not dispute that some recreatiuonal battery users utilize a "no load" test, but thats not a testing methodology people that work on live industrial battery systems for a living generally use. At least not in the telecommunications, or power industries.

I could stand corrected though. In the last 100+ years of battery system maintenance history the nice folks at the phone company have learned allot about battery maintenance, but clearly not everything.
I know you have extensive background in all of this....

But for me and a boatload of other captains/marine techs out there....we know it's not really a great test of battery health...most of us load test when in doubt...but a real rough rule of thumb is if you shut off your battery charger and put a couple light loads on it for a few minutes...if you aren't seeing somewhere between 12.5 and 12.6 I would pull out a load tester of devise another load testing strategy.

Doesn't work all the time...but many use it a lot. If I was responsible for keeping systems with the reliability you need...sure other tests are much superior.
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Old 06-26-2013, 04:56 PM   #13
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Right from EXIDE battery website...crap I know but there's a shread of truth to it.

Checking Battery Condition
Carefully, examine the battery externally.

o
Watch for terminal corrosion on the battery and make sure all connections are clean and tight.

o
If you see any cracks or holes in the container, cover or vents, we recommend you have your
battery replaced.

During regular service intervals, ask your technician to test your battery. This type of test can be
performed quickly by most automotive service centers. These tests will determine your batteries health
by measuring its “State-Of- Charge”.

Determining State-Of-Charge
12.75 & Above 100% Charged
12.60 to 12.74 85% to 100% Charged
12.40 to 12.59 75% to 85% Charged
12.20 to 12.39 50% to 75% Charged
12.00 to 12.19 25% to 50% Charged
11.99 & Below Fully Discharged
Note: The state of charge listed is an approximation. The relationship between state of charge and voltage vary
by CCA rating and case size.

http://www.exide.com/Media/files/Dow...0condition.pdf
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Old 06-26-2013, 05:36 PM   #14
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Right from EXIDE battery website...crap I know but there's a shread of truth to it.

Checking Battery Condition



Carefully, examine the battery externally.
o


Watch for terminal corrosion on the battery and make sure all connections are clean and tight.
o


If you see any cracks or holes in the container, cover or vents, we recommend you have your
battery replaced.


During regular service intervals, ask your technician to test your battery. This type of test can be
performed quickly by most automotive service centers. These tests will determine your batteries health
by measuring its “State-Of- Charge”.
Determining State-Of-Charge
12.75 & Above 100% Charged
12.60 to 12.74 85% to 100% Charged
12.40 to 12.59 75% to 85% Charged
12.20 to 12.39 50% to 75% Charged
12.00 to 12.19 25% to 50% Charged
11.99 & Below Fully Discharged
Note: The state of charge listed is an approximation. The relationship between state of charge and voltage vary

by CCA rating and case size.

http://www.exide.com/Media/files/Dow...0condition.pdf



Very interesting. I guess there is a difference between what manufacturers tell consumers on their public web sites and what they write in their industrial battery maintenance manuals.

I guess for consumers and automotive batteries they write for the average consumer to check their battery themselves.

Thanks for posting that. At least I know where the information is coming from now. I thought it was just another internet myth.
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Old 06-26-2013, 05:43 PM   #15
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Quote:
Originally Posted by ksanders View Post
Very interesting. I guess there is a difference between what manufacturers tell consumers on their public web sites and what they write in their industrial battery maintenance manuals.

I guess for consumers and automotive batteries they write for the average consumer to check their battery themselves.

Thanks for posting that. At least I know where the information is coming from now. I thought it was just another internet myth.
[/LEFT]
Many boaters struggle with batt switches in general...the thingies at the end of them are a total mystery...
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Old 06-26-2013, 09:16 PM   #16
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Thanks everyone for this great thread. Very relevant for me right now!
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Old 06-26-2013, 09:29 PM   #17
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The Exide table is much like the one in Ed Sherman`s book.
I use voltage as a basic indicator of need to investigate.
If unsealed, do a hydrometer test.
Skidgear, You looked after them, even equalizing regularly, 5-6 years service is your reward, I think they are just getting old.
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Old 06-26-2013, 11:18 PM   #18
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This is a great discussion. Very informative.
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Old 06-26-2013, 11:27 PM   #19
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I had been using the voltage scale as a guide to state of charge. That I found is all it is----a guide. Since installing a state of charge meter, I have found that house batteries are seldom without load. When they are under load they will read less voltage than when resting. I think you will find that at times your batteries are reading lower then bounce back when a big load is removed. The SOC meter counts amps in and amps out to give a true state of charge. A really great tool worth the money and trouble to install.
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Old 06-27-2013, 05:53 AM   #20
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A Volt mater will give notice of a problem , but each cell must be tested by specific gravity (with a temp gauge) to actually know what is going on.

All wet batts die slowly thru internal losses.

A new batt will loose 1/2% a day , an old batt perhaps 3% per day.

After 6 years these are definiatly OLD and after a hydrometer check I would look at the charge voltage , sounds like it could be low also.

Beware if the boat is old and has a "converter " which was designed to hold up the voltage with AC power in port and not require frequent watering.

A real battery charger will recharge your batts , the "converter " style may take a week or more.
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