Batteries going bad? - SailNet Community
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post #1 of 14 Old 07-21-2008 Thread Starter
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Batteries going bad?

We've recently done a number of upgrades to the electrical system, including new panel and reconnecting some gear that came with the boat wen we bought her, but were never hooked up, i.e. a Heartlink10 monitor. We have 3 3-year-old group 27 batteries in the house bank. For those not familiar, he Heartlink uses a shunt on connected to the ground. All equipment that is connected to the house bank goes through that shunt so the monitor can measure the amp hours used. It measures the drain when devices are running and, when charging, it measures the amount of replenishment going on. It compares its measured usage with the amp hours you tell it that your bank has via configuration and displays the state of charge in a manner similar to a fuel gauge, e.g. half full. So when it says the bank is half full, what it means is that you have used half of the capacity it thinks the bank has.

Here's my question: After a weekend of cruising, the Heartlink says the bank is full, that I've hardly used any of its capacity, but when I check the voltage of the battery, it is below 12v, around 11.8v. When fully charged, the bank voltage reads close to 13v. I thought that when the voltage goes below 12, you're pretty well depleted. Does this mean that my batteries are unable to hold a full charge anymore, and are therefore running out of charge with very little usage? If so, does that mean they are nearing end of life? Any insight into how to read these various signs will be much appreciated.

TIA
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post #2 of 14 Old 07-21-2008
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Joel...assuming you have nothing on your negative house terminal except the shunt and you aren't using your start battery in the measurement process (ie switched to BOTH)...there are several possibilities:
1. You have entered the wrong overall capacity for your group 27's...should be around 250-270 amp hours total.
2. You have SOMETHING in the DC system on while you are reading your link. Check current time amp use on meter before checking voltage. Voltage should ONLY be measured when everything is off for a while on the boat.
3. The batteries are old and have lost capacity to hold a charge. If you have flooded batteies, the BEST way to check this is with a "turkey baster" hydrometer sold for 10 bucks at any auto store. The other thing you can do is chrge the batteies fully and leave EVERYHING in the boat off for 12 hours after charging. Then use your link to measure voltage. If the batteries are good you should see 12.6V minimum. Any less and you have dying batteries or dead ones. A reading of 11.8 is exceptionally low and corresponds to near total depletion of the battery bank...which is possible if you used 200ah's or so between charging. If you have refrigeration this can easily soak up 150ah's in a couple of days alone.

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Thanks. I used 270 as the overall capacity. I was under sail at the time I was reading the voltage, so I had the GPS, autopilot, VHF and depth on. I also have the stereo's memory wired to the hot side of the main bank circuit so it's never off, but that should be minimal. I use the Blue Seas dual circuit switch, so it's never set to BOTH, but the ACR combining relay does combine when charging. I wasn't charging during the readings, though. We had the refrigeration on for about 12 hours on Saturday and only ran the engine for maybe an hour that day. Yesterday we ran for about an hour and a half at the end of the day and ran no refrigeration, so hopefully I'm fully charged. The bank read 13v when we were back at the mooring. They are flooded batteries and I think I have a hydrometer around somewhere. I thought I heard of a load test that can determine a battery's ability to hold a charge.

Thanks again.
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post #4 of 14 Old 07-21-2008
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A hydrometer is a good way to go.

If you want to use voltage to determine condition, there are two test - resting voltage and load voltage.

Resting voltage... After charging your batteries for a while turn the charger off. Let the batteries rest with no load on them for 24 hours. Check the voltage at the battery with a meter. 12.7 volts is a full charge. 12.3 volts is about 50%. 11.7 volts is a dead battery. (This method assumes a temperature of about 70 F).

Load voltage... Again the batteries need to be charged first. Then the surface charge must be removed. To do this put a small load on the battery for 10 minutes (run the refrigerator and cabin lights). Then attached the load tester. Turn it on and then adjust the load. You should be able to pull 1/2 of the CCA rating (look on the battery label) for the battery for 15 seconds without going below 10.5 volts. You'll have to buy, rent, or borrow a load tester.
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post #5 of 14 Old 07-21-2008
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I should have added that you should disconnect and test the batteries individually.
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post #6 of 14 Old 07-21-2008
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Joel...after your post #3 explanation...it is clear you took a voltage reading when the batteries were under load so that is why you got such a low reading. The hydrometer is the cheap and easy way to check battery state so there is no need to go beyond that with a load test if the individual cells...check EACH one!...are in good condition and you are not experiencing any real difficulties in holding a charge AND the batteries come up a bit after being used in normal operation.
Since you are using 270 as your working capacity...that gives you 135 ah's till you are 50% discharged in theory. Try fully charging your batts at the dock then using stuff on your boat till the link tells you that you're down 135AH's. Then turn off EVERYTHING (except the car stereo memory) and wait an hour. The Volt reading on the link should be in the 12.2 or 12.25 range if the batteries are indeed in excellent shape. If the batts are under 12V you have lost significant capacity. If this is the case you can live with them until they just get too bad, or replace them..but if you do so, replace ALL 3 at the same time.

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post #7 of 14 Old 07-21-2008
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I had a conversation with a rep from a battery manufacturer just yesterday. He said "Batteries never die, They are murdered."

Over charging, under charging, improper charging are the criminals.
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post #8 of 14 Old 07-21-2008
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bubb2,

He stole my stuff!!

A couple of years ago I participated in a seminar at the Annapolis SSCA Gam with Scott Berg and Nigel Calder on boat electrical systems. The first slide I used was:

* Most batteries on boats don’t die a natural death. They are murdered.

* The usual suspects are: undercharging, overcharging, ignorance, and neglect.

* Together, these suspects account for almost 90% of the battery murders onboard.

* The prudent mariner will ask, “Is there a murder in progress aboard MY boat?”


Great minds, and all that :-))

Bill
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Quote:
Originally Posted by btrayfors View Post
bubb2,

He stole my stuff!!

A couple of years ago I participated in a seminar at the Annapolis SSCA Gam with Scott Berg and Nigel Calder on boat electrical systems. The first slide I used was:

* Most batteries on boats don’t die a natural death. They are murdered.

* The usual suspects are: undercharging, overcharging, ignorance, and neglect.

* Together, these suspects account for almost 90% of the battery murders onboard.

* The prudent mariner will ask, “Is there a murder in progress aboard MY boat?”


Great minds, and all that :-))

Bill
I wish i was at your seminar as I would have learned more!
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Guilty as charged (all puns intended), at least on ignorance and neglect. Last year I didn't check electrolyte level once. This spring, I had to add over a half gallon (combined) of distilled water into the 3 flooded cell batteries that make up the house bank. Also, I leave them on board all winter. I keep the level of charge up, but that can't be good.
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