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Old 02-21-2015, 08:25 AM   #1
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battery decline over time

Any rule of thumb I can use to estimate the decline of stored amps over time? I cruise full time and at anchor most of the time. I don't have the option to let my batteries sit to get a true voltage reading. I have 4 6v for a total of 440 amps 18 months ago. I measure usage with a Victron meter which measures amps used and replaced via a shunt. I never discharge below 80%. My SOC is based on the original 440 amps but what might that be now?
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Old 02-21-2015, 09:28 AM   #2
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Side question. Do you equalize your batteries very often? I notice a major difference in capacity if I do not equalize for 60 days
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Old 02-21-2015, 09:56 AM   #3
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Meridian, you didn't state what your usual charge cycle is like. Are you plugged into shore power and charging overnight, do you charge off the engines when running, etc...
This could have a major difference in how the batteries hold up long term.
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Old 02-21-2015, 10:36 AM   #4
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There is no rule of thumb about age vs capacity deterioration. Some don't deteriorate at all and some drop drastically over time. In some cases it is due to a poor charger or a poor battery. In others it is inexplicable.

But since all golf cart batteries have removable caps on the top, you can use the specific gravity as a good indicator of state of charge. Much more accurate than resting voltage.

So buy a hygrometer or SG meter specifically designed for batteries. Look on this page- http://www.amazon.com/s/ref=nb_sb_ss...ery+hydrometer There are two basic types: floating glass bulb and rotating pointer. Either work well.

Google "Trojan battery specific gravity chart" to find a chart that gives SG vs state of charge. Then with your batteries fully charged check the specific gravity to see if it matches Trojan's chart. If not, then your batteries may be degraded. For this test, check all cells to look for one or two that are significantly lower than the others. That indicates a sulfated cell and it is time to replace that battery. When you do the test described below check a couple of cells and average the reading before looking up on the Trojan chart.

To find out how much whether the SG at full charge is correct or not, do this test. Run the batteries down with a known load for ten hours. It would be best if that load is 440/20=11 amps as a 20 amp hour discharge rate is the basis for the 440 amp hour rating of your batteries. Use multiple incandescent lights to achieve 11 amps. Then at the end of 10 hours the batteries should theoretically be 50% discharged. Measure the specific gravity after waiting an hour to let any gasses dissipate. If it is lower than what it should be according to the Trojan chart, then you have less capacity. You can eyeball how much by looking at the chart. If the chart says that the SOC is 25% and it should be 50% then your batteries have roughly 220/.75= 290 real amp hour capacity.

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Old 02-21-2015, 10:51 AM   #5
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Degradation is pretty easily measured given an accurate resting voltage measurement (Charge, let sit for a day (70 degrees or so) with no load, then measure voltages.)
For instance, using the below meter references, if your voltage is at 75% you'll have about that percentage of your fresh bank capacity. Discharging to 50% means 110 amp hours or so of usable power from the original 220...



Meters like the Victron loose some accuracy over time. The Balmar Smartcharge meter appears to be the most accurate from a Battery "Fuel" gauge perspective..
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Old 02-21-2015, 11:02 AM   #6
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Capacity decay for batteries is linear for the most part if they are charged and discharged according to the manufacturers specs. Sla and agm average about 4%/yr. so after 5 years you'll be looking for new. A capacitance test annually can let you know how you've been treating them. Set your soc cap number to 410 and you should be ok.


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Old 02-21-2015, 11:04 AM   #7
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Quote:
Originally Posted by Heron View Post
Degradation is pretty easily measured given an accurate resting voltage measurement (Charge, let sit for a day (70 degrees or so) with no load, then measure voltages.)
For instance, using the below meter references, if your voltage is at 75% you'll have about that percentage of your fresh bank capacity. Discharging to 50% means 110 amp hours or so of usable power from the original 220...



Meters like the Victron loose some accuracy over time. The Balmar Smartcharge meter appears to be the most accurate from a Battery "Fuel" gauge perspective..
I'm with D Marchand on this topic, SpG is the best plus it gives you individual cell health, often a precursor to failure way before a meter picks it up.

Relying upon several different meters and connections and throwing in a connected inverter or 3 can get confusing. That said, I monitor my Magnum BMKs and will break out the hydrometer when and if something seems amiss. Two checks if you will, one good but one better.
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Old 02-21-2015, 11:47 AM   #8
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Thanks for your support Sunchaser. In addition to the OP stating that he lived aboard full time and couldn't let his batteries sit long enough (about 4 hours) to get a decent voltage reading, SG is always more accurate than voltage measurements.

He can do the test I described above during a day where he starts early in the morning and finishes by nighttime. He can turn on or off light bulbs to maintain the 11 amps if he uses another appliance. He should manually cycle his fridge during this test to make that work.

FWIW I did this exact test when cruising myself. My batteries were 20% degraded after a couple of years.

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Old 02-21-2015, 12:00 PM   #9
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Now in my 60's I've been utilizing wet cell batts of all brands, types, and sizes in cars, trucks, equipment, boats… etc. Still do!

In my early years I spent considerable time performing all sorts of tests to see how my batts are doing during their life and how I might improve their performance and length of service. Eventually I realized… as long as they are hooked up correctly and maintained and used as advised by manufacturer (from onset) that all the "testing time" was wasted… i.e. the batts would be as they will be. Your batts are going to eventually fail - period.

So… relax, simply service them well and use good brand batts correctly; replace when required.

Of course, if you get your jollies out of hours of incidental battery testing… carry on!

Happy Batt Daze! - Art
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Old 02-21-2015, 01:22 PM   #10
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Art, I'll take your advice. Too much other stuff to do in the Exumas this time of year.
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Old 02-22-2015, 07:49 AM   #11
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.I would purchase and install a SOC meter, a gas gauge for house batts.

80% discharged is HUGE hit for most LA (lead acid) batts.

50% is considered the normal for longest life.

Most cruisers batts die more rapidly as the cycle life is figured on recharging to 100% or even 115% after Every discharge , with no sitting half dead before recharge.

This is not the way most folks cruse , so 50% to 85 charged becomes the norm .

Eventually 85% becomes the fully charged capacity , and the short charge cycle begins again.

Solar is a great help, if the solar gets to top up from 85% to 100%+

Some folks have found a de-sulphator in the system , while charging does help.
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Old 02-22-2015, 08:27 AM   #12
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Couple of things to add....

Re your discharge regime, do you dischange them 80% leaving 20%, or discharge them by 20% leaving 80%? With a 400AH bank, I'm guessing the former which is definitely pushing the batteries pretty hard.

Re SG readings, that is indeed the best way to tell the state of charge. But if it's low, it may not indicate a failing battery, but just a battery that isn't being brought back to full charge. Try an extended charge, or better yet an equalize cycle to see if you can get the charge level up where it belongs. A sulfated battery will typically show voltage reflective of full charge, but low SG. If the sulfation isn't too bad, equalization will bring it back.

Circling back to your original questions, failing batteries is typically either because they have not been getting regularly returned to full charge and have become irreversibly sulfated, or because they have just worn out. The worn out part is based on how many amp-hours you have run through the battery over it's life. All the manufacturers express this in terms of the number of cycles you can get at various levels of discharge. When you do the math, it turns out there is a pretty constant number of Ah that you can run through a battery. You can either do it via a large number of small cycles (low depth of discharge), or a smaller number of big cycles (larger depth of discharge). You get to pick.
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Old 02-22-2015, 09:55 AM   #13
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Quote:
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So… relax, simply service them well and use good brand batts correctly; replace when required.

Of course, if you get your jollies out of hours of incidental battery testing… carry on!

Happy Batt Daze! - Art
Art is correct, don't worry be happy. Just one point though, SpG testing does not take hours. Whether from year 3 or 5 of battery age, when checking electrolyte level have your hydrometer handy and check each cell - quick and easy. Maybe once per year until a problem appears then more frequently.

My first set of LAs we're going strong after 8 years, but time to pitch them as extended cruise time loomed. If I were not extended cruising and close to the marina I'd run mine to SpG or operating problem destruction time. This could take 10 years with a good charger and moderate battery use. Having once been in the battery business, my take is there are good, better and best - not reflective of price either. If in doubt, buy Trojan.

So yes Art, nothing complicated.
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Old 02-22-2015, 12:18 PM   #14
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Art is correct, don't worry be happy. Just one point though, SpG testing does not take hours. Whether from year 3 or 5 of battery age, when checking electrolyte level have your hydrometer handy and check each cell - quick and easy. Maybe once per year until a problem appears then more frequently.

My first set of LAs we're going strong after 8 years, but time to pitch them as extended cruise time loomed. If I were not extended cruising and close to the marina I'd run mine to SpG or operating problem destruction time. This could take 10 years with a good charger and moderate battery use. Having once been in the battery business, my take is there are good, better and best - not reflective of price either. If in doubt, buy Trojan.

So yes Art, nothing complicated.
Sun - Thanks, You are Exactly Correct!! Don't Worry Be Happy!

Also, If I May Say... "Walk softly but carry a big stick!" Thanks, Teddy!!
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