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Old 02-03-2009, 13:10   #1
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Concerning Batteries

Two easy questions this time.

1. How do I know when my batteries are 100% fully charged? (other than staying on shore power for a week)

2. How do I know when a battery is ready to be replaced?
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Old 02-03-2009, 14:28   #2
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Good God!



Try Search and Batteries. The subject has been flogged to absolute death.
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Old 02-03-2009, 14:32   #3
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Old 02-03-2009, 15:16   #4
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Quote:
Originally Posted by Aquah0lic View Post
Two easy questions this time.

1. How do I know when my batteries are 100% fully charged? (other than staying on shore power for a week)

2. How do I know when a battery is ready to be replaced?
Your boat probably has a volt meter installed near the batteries; if not a handheld will do fine. The batteries should be around 13.5 volts when fully charged (it can very a bit, but shouldn't be lower than 13.5).

Turn your battery switch to "Off", and then check the batteries again in a day or two. If they're still at 13.5, you're great. If they've dropped, something's wrong. The idea here is you're checking to see if they hold their charge.

A common causes for bad batteries (if you're dealing with standard lead-acid) is running out of water. If you open the cells on the top, the fluid should be covering tops of the plates. If they're exposed, that's a problem. If you've treated your batteries poorly for sometime, you might want to entertain the idea of just replacing them and starting off on a proper maintenance schedule as of now.
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Old 02-03-2009, 16:27   #5
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Battery 101

http://www.trojanbattery.com/Product...nglish_001.pdf

Surrette/Rolls website also has some good info.
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Old 02-03-2009, 16:52   #6
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Batteries which are at the end of their life won't hold the full up change very long even when they DO take a charge. You can think of a battery like a glass which you fill with water (amps) by charging it and use the water when you turn lights, instruments, etc on and draw those stored amps.

An old battery is like a glass full of sand. There is less volume for water - capacity has gone down and when you use the water it "empties" faster. The process of losing capacity is somewhat "inevitable" and there are theories about how to best maintain the capacity. Batteries are often rated in cycles and presumably if you keep them fully charged or close to it you might extend the life. I am sure others disagree and believe that you need to discharge and then fully recharge.

How old are your batts?
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Old 03-03-2009, 06:53   #7
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Originally Posted by svHyLyte View Post


Try Search and Batteries. The subject has been flogged to absolute death.
There are 2 reasons I ask instead of search. First, I am underway and have a very slow internet connection(when I can get one) and limited battery power to dig through the archives. Second, even though there's the occasional jerk who berates me for asking dumb questions, there's always some decent people who will try to help.
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Old 03-03-2009, 06:56   #8
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Batteries which are at the end of their life won't hold the full up change very long even when they DO take a charge. You can think of a battery like a glass which you fill with water (amps) by charging it and use the water when you turn lights, instruments, etc on and draw those stored amps.

An old battery is like a glass full of sand. There is less volume for water - capacity has gone down and when you use the water it "empties" faster. The process of losing capacity is somewhat "inevitable" and there are theories about how to best maintain the capacity. Batteries are often rated in cycles and presumably if you keep them fully charged or close to it you might extend the life. I am sure others disagree and believe that you need to discharge and then fully recharge.

How old are your batts?
Good analogy!
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Old 03-03-2009, 06:58   #9
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Battery 101

http://www.trojanbattery.com/Product...nglish_001.pdf

Surrette/Rolls website also has some good info.
Thanks DF, excellent resource.
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Old 03-03-2009, 07:06   #10
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Just a correction to Rebel Hearts post. Once charged and floated at 13.3-13.5 volts, the battery voltage WILL drop over the next 24 hours to 12.6-12.7Volts which IS a 100% charge (if left unused). The difference between the 2 voltages is a surface charge from charging and NOT actually a battery voltage reading. 12.6-12.7V is 100%!!
Note...surface charge may be wiped out by placing a 20amp load on the battery for 10-15 minutes.
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Old 03-03-2009, 08:12   #11
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Correct!

And, just to underscore what may have been missed, the ability of a battery to "hold a charge", i.e., to show relatively high voltages for some time after charging says very little about the capacity of the battery. As DefJef's analogy suggests, a battery may seem normal in terms of voltages seen but may indeed have lost a great deal of it's capacity (i.e., it's ability to deliver rated power over time).

Bill
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Old 03-03-2009, 08:37   #12
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Aquah0lic--

When launches oneself off on a great adventure it is all well and good to be willing the rely on the largess of others, but not to be dependant upon it. It is wise to prepare oneself beforehand, at least somewhat, so that one does not find oneself sinking in an anchorage for a spun off locking nut on a shaft log and no internet connection in sight. In the time it took you to pose your question you could have done a simple google search--and had your answer. In fact 14,600,000 in .28 seconds.

Never-the-less, as posted by others, one can test the state of charge of a lead acid battery (or battery bank) with a multimeter simply by measuring the voltage however this is not always an accurate indicator. More accuracy is provided by measuring the specific gravity of the electrolyte in the battery (assuming that the battery is not of the sealed type).

Specific gravity is measured with a hydrometer--available very inexpensively at AutoZone/Napa/or most any good hardware store. Simply draw the battery acid into the hydrometer so that the float is not touching the sides, top or bottom of the barrel. Take the reading with your eyes level with the surface of the drawn up liquid, and then subtract 0.004 for each 10F above or below 75F. Do this for each of the cells of the battery.

State of Charge/Specific Gravity
100% charged/1.265
75% charged/1.239
50% charged/1.200
25% charged/1.170
Fully discharged/1.110

You would do well to invest in copies of Nigel Calder's "Boat Owner's Mechanical and Electrical Guide"; "Marine Diesel Engines"; and, "Boatowner's Practical and Technical Cruising Manual". These can be obtained used, quite inexpensively.

FWIW...

s/v HyLyte
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Old 03-03-2009, 08:49   #13
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Also, what kind of batteries? AGM's and Gel's have a different voltage when fully charged than flooded cells.
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Old 03-03-2009, 09:59   #14
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Originally Posted by camaraderie View Post
Just a correction to Rebel Hearts post. Once charged and floated at 13.3-13.5 volts, the battery voltage WILL drop over the next 24 hours to 12.6-12.7Volts which IS a 100% charge (if left unused). The difference between the 2 voltages is a surface charge from charging and NOT actually a battery voltage reading. 12.6-12.7V is 100%!!
Note...surface charge may be wiped out by placing a 20amp load on the battery for 10-15 minutes.
Thanks, Cam. That was the part I was mostly confused about. You cleared it up nicely.
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Old 03-03-2009, 10:01   #15
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Originally Posted by svHyLyte View Post
Aquah0lic--

When launches oneself off on a great adventure it is all well and good to be willing the rely on the largess of others, but not to be dependant upon it. It is wise to prepare oneself beforehand, at least somewhat, so that one does not find oneself sinking in an anchorage for a spun off locking nut on a shaft log and no internet connection in sight. In the time it took you to pose your question you could have done a simple google search--and had your answer. In fact 14,600,000 in .28 seconds.

Never-the-less, as posted by others, one can test the state of charge of a lead acid battery (or battery bank) with a multimeter simply by measuring the voltage however this is not always an accurate indicator. More accuracy is provided by measuring the specific gravity of the electrolyte in the battery (assuming that the battery is not of the sealed type).

Specific gravity is measured with a hydrometer--available very inexpensively at AutoZone/Napa/or most any good hardware store. Simply draw the battery acid into the hydrometer so that the float is not touching the sides, top or bottom of the barrel. Take the reading with your eyes level with the surface of the drawn up liquid, and then subtract 0.004 for each 10F above or below 75F. Do this for each of the cells of the battery.

State of Charge/Specific Gravity
100% charged/1.265
75% charged/1.239
50% charged/1.200
25% charged/1.170
Fully discharged/1.110

You would do well to invest in copies of Nigel Calder's "Boat Owner's Mechanical and Electrical Guide"; "Marine Diesel Engines"; and, "Boatowner's Practical and Technical Cruising Manual". These can be obtained used, quite inexpensively.

FWIW...

s/v HyLyte

Thanks for that added input. You are forgiven.
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