Battery readings

[Tally Ho]

So, I posted earlier about the value of a voltage meter (analog) and the feedback I got led me to purchase a digital volt meter instead (hand held) for checking my batteries....

I have 2 batteries, off the boat for the winter. I had them on float chargers for a while, and then disconnected them and have been taking voltage readings every 24 hours. Here is what I recorded:

Batt 1 - Deep Cycle Batt 2 - Starting Battery
13.77 13.97 I had both batteries on float charger at this point
13.78 14.17 At this point, I disconnected the flat chargers
13.02 13.39 24 hours off the charger
12.86 13.04 another 24 hours no charger
12.81 12.89 another 24 hours no charger
12.77 12.81 another 24 hours no charger
12.76 12.77 another 24 hours no charger

What do these voltage readings tell you? Do these readings look "normal" for a healthy battery?

Both batteries are Group 24. Batt 1 has a 2009 "Battery Checked" sticker on it, but not sure of age. Batt 2 appears to have been purchased in 2010.

Greg

 

[Bill Roosa]

Well at the risk of starting a heatd discussion. IMHO you probably have dirty battery tops. Have you cleaned and flushed with clean water the battery outer casing?
Even a small amount of dirt and grim can cause "self discharge" like you are seeing.
I'd be heastant to make a call just based on these voltage values. Clearly there are no bad cells. I'd recommend continuing to take reading to see if the change in voltage flattens out after a week or so.

 

[Dan Hill]

After a battery is removed from a charge cycle they have whats called a surface charge. A fully charged battery is said to hold a voltage of 12.74, which your still above after what 5 days static. Your batteries are just shedding that surface charge. I would say they are fine and wouldn't hesitate using them.

 

[Stu Jackson]

I agree, but to reinforce (not replace) your readings, get hydrometer readings of each cell, not too hard to do.

 

[Maine Sail]

1- What were the temps of the batteries when measured?

2- Have you cleaned them?

3- Your voltages are reading slightly high so your meter could be off (not uncommon)..

4- An SG reading would be more accurate but you need a good hydrometer, not one with the little floating balls. I prefer a sight refractometer for specific gravity readings but they cost over $100.00 for a decent one.

5- What does your battery manufacturer consider a "full" battery for OCV?? Every battery is going to be slightly different, Trojan, for example, is 12.73V (resting voltage) for wets.. Without an accurate meter it is very tough to tell the difference between 12.70 and 12.80 but you can get a "ball park"...

If batteries are cold it is not unusual for them to hold a surface charge for significantly longer than in warmer temps. If they are cold they should stabilize somewhere around 12.7 +/-...

Our wet batteries are at 12.73V when full. At about 75 - 80 degrees it takes a little over 24 hours for them to come to a resting voltage. In the cold they can still be showing over 13V after multiple days. Our charger has not been on in over a week and our batts were still showing 12.82V yesterday or more than full. You can't be "more than full" but you can have a residual surface charge.. Colder temps can really slow the surface charge from dissipating..

Also voltage tells us zip, zilch & nada about the batteries actual current state of "capacity". You can have a full 100 Ah battery, reading 12.73V that can only deliver, due to age and abuse, 10 Ah's....

 

[Dan Hill]

MS is spot on as usual, listen to the master! Hey Maine Sail, you ever eat @ Norms in Portland? Best Lobstah bisque I've ever tasted! The fire roasted flat bread rocked also. Now back to voltage and electrolyte discussions

 

[Blindnavigator]

Anything 12.65v or higher after resting suggest they're fine, according to several sources

 

[Benny17441]

It looks like they are fine but perform a load test to confirm they are holding charge. Easiest way is to take them to your local auto shop retailer and have them tested.

 

[Tally Ho]

Well at the risk of starting a heatd discussion. IMHO you probably have dirty battery tops. Have you cleaned and flushed with clean water the battery outer casing?
Even a small amount of dirt and grim can cause "self discharge" like you are seeing.
I'd be heastant to make a call just based on these voltage values. Clearly there are no bad cells. I'd recommend continuing to take reading to see if the change in voltage flattens out after a week or so.

Battery posts are clean. I checked them today, and looks like they are "flattening" out.....both batteries read 12.76.

Greg

 

[Tally Ho]

I agree, but to reinforce (not replace) your readings, get hydrometer readings of each cell, not too hard to do.

How can you do that on a "sealed" ? I can't even check the acid level.

Greg

 

[Tally Ho]

1- What were the temps of the batteries when measured?

2- Have you cleaned them?

3- Your voltages are reading slightly high so your meter could be off (not uncommon)..

4- An SG reading would be more accurate but you need a good hydrometer, not one with the little floating balls. I prefer a sight refractometer for specific gravity readings but they cost over $100.00 for a decent one.

5- What does your battery manufacturer consider a "full" battery for OCV?? Every battery is going to be slightly different, Trojan, for example, is 12.73V (resting voltage) for wets.. Without an accurate meter it is very tough to tell the difference between 12.70 and 12.80 but you can get a "ball park"...

If batteries are cold it is not unusual for them to hold a surface charge for significantly longer than in warmer temps. If they are cold they should stabilize somewhere around 12.7 +/-...

Our wet batteries are at 12.73V when full. At about 75 - 80 degrees it takes a little over 24 hours for them to come to a resting voltage. In the cold they can still be showing over 13V after multiple days. Our charger has not been on in over a week and our batts were still showing 12.82V yesterday or more than full. You can't be "more than full" but you can have a residual surface charge.. Colder temps can really slow the surface charge from dissipating..

Also voltage tells us zip, zilch & nada about the batteries actual current state of "capacity". You can have a full 100 Ah battery, reading 12.73V that can only deliver, due to age and abuse, 10 Ah's....

1) Batteries are about 65 degrees ambient temp in my basement.
2) No, I have not cleaned them, but they are nice and shiny (hell of a lot better looking than my car batteries ;-)
3) Could be....cheap $10 Digital Multi Meter. Can't find a way to calibrate it
4) How do you check a sealed battery?
5) I will have to research the 2 manufacturer sites and see if I can get that info

Tonight they both read 12.76, so it seems as though they are about at normal charge. I will monitor them for a few more days.

Since you are the Zen Master, what about a load test? Can I do that at home? I did take both batts to my local auto parts store shortly after haul out and asked them to check the batteries. Not sure what they did (hooked them to a machine for a few minutes) and said they were fine. Does that sound like enough time to do a load test?

Thanks for all the good information I read a lot of your posts and you are quite thorough and obviously knowledgeable.

Great help to a novice like me.

Greg

 

[Maine Sail]

How can you do that on a "sealed" ? I can't even check the acid level.

Greg

You can't...

 

[Tally Ho]

It looks like they are fine but perform a load test to confirm they are holding charge. Easiest way is to take them to your local auto shop retailer and have them tested.

I did take them to a auto parts store and they hooked them up to something, and a few minutes later said "they are good". How long does it take to do a load test? A few minutes?

Greg

 

[Bill Roosa]

there are different types of load test. The standard auto battery (lots of power short term and not much deep cycle capability) test is to load the battery with a 100ish amp load and watch the voltage. If it "goes into the red after 10 seconds" it is bad. It is a pretty good test for auto batteries. For a deep cycle battery is will confirm wellness but it it fails it does not mean it is bad. There is no deep cycle tester that I know of but you could just load the battery with a C/20 load and watch the voltage. The test will take much longer and I would note that a C/20 load is not that uncommon in boating use so you can just monitor your voltage/load duration all the time and get a feel for the battery health.

 

[H30Gary]

Bil-
I'm curious - What's a C/20 load?
Thanks,
Gary

 

[Mike Culik]

Greetings,

You can buy a battery load tester at Harbor Freight cheap, about $25.00
http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-90636.html

They are good enough to load down the battery to show if there is a shorted or sulfated cell. Just a voltage reading will not....

Between monitoring the voltage with a digital meter and the above test once a year, I am confident of my batteries.

Also, IMHO any battery over 4 years in a boat should have a backup or be monitored closer.

Cheers, Mike

 

[Maine Sail]

Bil-
I'm curious - What's a C/20 load?
Thanks,
Gary

Gary,

A C/20 load is battery capacity in Ah's at the 20 hour Ah rating. To figure the 20 hour "load" you divide "C" by 20.

Eg: 100Ah Battery / 20 = 5A

or

Eg: 150Ah Battery / 20 = 7.5A

To test for Ah capacity you would apply the C/20 load until the battery falls to 10.5 volts. You should be able to apply a 5A load to a 100Ah battery for 20 hours before it hits 10.5V when new and freshly broken in.

There are many types of tests:

Capacitance Test: This test is done with an expensive analyzer such as those made by Midtronics. It tests the internal resistance of the battery and analyzes condition based on this and some other factors. These have become the defacto analyzers for determination of battery warranties. The test takes less than 60 seconds. A battery is considered no good if it can't produce 80% of new rated cranking capacity.

Pulsed Load Test: Using complex computer algorithms, an electronically pulsed load, and the data you plug into the analyzer, it gives you the batteries actual CCA capacity automatically compensated for temp. A battery is considered no good if it can't produce 80% of new.

Carbon Pile Load Test: These are the traditional load tests where a load of 50% of CCA capacity is applied for 15 seconds. An 800 CCA battery would get a 400A load for 15 seconds. As you can see by this test standard a 100A load on an 800CCA battery won't tell you much. A 500+A carbon pile is needed for many batteries these days. The battery voltage needs to remain in the "OK" range, based on temp, or the battery is failed. Many deep cycle batteries do not publish a CCA but many manufacturers will tell you what they can do in terms of CCA, if you call them, so you can apply the correct load. These testers have gone out of style but can still be pretty reliable. Either a capacitance or pulsed load tester will give you the CCA so you can then apply a proper carbon pile test.

Reserve Minutes Capacity Test: A 25A load is applied to the battery and run for the rated Reserve Minutes that are published on the battery. The test is over when the voltage hits 10.5 volts. If you don't get more than 80% of the rated minutes the battery can be considered un-passable.

Basically a battery that has lost more than 20% of it cranking amps or capacity can be considered ready for the "recycle bin"... This does not mean they are dead, dead just that what batteries get to this level of "compromised state" the predictability of them becomes a crap shoot. Sometimes they go another year sometimes they fail within a few weeks...

If you want them tested try to find a shop that uses a Midtronics capacitance tester or Argus pulsed load tester as these are considered the most reliable "quick" tests.