Simple Battery theory test

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BlueSkyNick

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Further to my pre-Christmas thread about the state of my batteries, I have been doing some more measurements.

In summary, I have 3 105Ah in one bank which have been delivering less than expected charge.

First, I made sure they were all fully charged - 14.0v being the max from my onboard charger, at 0.2A, for 24 hours. Then I switched the charger off and left the batteries for 3 days to settle. Today, their combined voltage was 12.77. I disconnected them from each other and measure between 12.7 and 12.82 on each, which is consistent.

Decided to start with a simple slow discharge on one battery, and connected a 25w nav light fitting, ie drawing 2amps. The voltage showed 12.45v with the bulb connected.

6 hours later I found the voltage was down to 10.2 !! WHen I removed the bulb, it slowly recovered to 12.2 ish.

I am now convinced this and probably the other two batteries are past their best (even though they are only 3 years old).

Am I wrong?
 
I am afraid at least the battery you tested id dead. Having only taken out 12 AHRS and drawing 2amps the voltage should have been way higher than 10.2V with the load on. Its not past its best its gone to god.
Sorry
Try charging and testing each battery separately, don't leave them connected together or in the system in case there is some unknown circuit draining them. If however one battery is OK you should not mix old and new batteries so you will need to replace them all anyway.
 
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Further to my pre-Christmas thread about the state of my batteries, I have been doing some more measurements.

In summary, I have 3 105Ah in one bank which have been delivering less than expected charge.

First, I made sure they were all fully charged - 14.0v being the max from my onboard charger, at 0.2A, for 24 hours. Then I switched the charger off and left the batteries for 3 days to settle. Today, their combined voltage was 12.77. I disconnected them from each other and measure between 12.7 and 12.82 on each, which is consistent.

Decided to start with a simple slow discharge on one battery, and connected a 25w nav light fitting, ie drawing 2amps. The voltage showed 12.45v with the bulb connected.

6 hours later I found the voltage was down to 10.2 !! WHen I removed the bulb, it slowly recovered to 12.2 ish.

I am now convinced this and probably the other two batteries are past their best (even though they are only 3 years old).

Am I wrong?

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Probably not. From what you say about the charging rate I would suggest they were not fully charged in the first place. The voltage reading does not fully indicate the charge level of the battery. I would suggest you re-charge them and get yourself a hydrometer and test/measure the SG of the electrolyte. If memory serves, when fully charged the reading will be in the order of 1280 ish, dropping back to 1275 when batts have rested. You can buy one for a few quid from the likes of Halfords.
They even have a coloured scale indicating the charge condition of the batt as being Flat/Fair/Fully Charged. Anyway, well worth the expenditure before you purchase new batts which you may not need. Good Luck.
 
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Any idea why there is a 2volt difference between load on and load off?

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This sort of high voltage drop with load is common with a dead battery. A 2v drop with only 2A current on this size battery is about as bad as it gets without almost complete failure.
3 years is not a great life. I would change battery type / brand if you have treated them reasonably and kept them above 50% discharge
 
Thanks for your comments. Unfortunately they are sealed batteries, else I would have measure the specific gravity already, so I can only go on the voltage and the actual capacity.

the details are in the previous thread I mentioned here http://www.ybw.com/forums/showflat.php/Cat/0/Number/2113131/an/0/page/2#2113131

I am reasonably convinced they are as fully charged as can be, without buying a higher voltage charger.
 
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Probably not. From what you say about the charging rate I would suggest they were not fully charged in the first place.

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As you point out 14v is not the ideal charge voltage, but if the batteries were only accepting 0.2A at 14V they must have been reasonably charged. Even if they were only 50% charged the battery only has a capacity of 24AHRS.
Charging the battery to a higher voltage occasionally at least will have a beneficial effect on the life of the batteries and you may want to consider a new charger with the new batteries.
 
I already have, as mentioned in my original thread. I fitted it about 6 months ago in my last but one attempt to save the batteries.

I shall refit it when I get new batteries, although notice that the latest battery chargers, from Sterling anyway, have a pulser built in to them.
 
If you take the battery you suspect as duff, to a battery supplier, he can test it with the new type of battery tester, that will show more info than a meter and hydrometer.

I have just had the car battery tested - duff - and replaced. It will show if the battery is beyond hope or just needs a good recharge.

By the sound of yours, it is probably full of sludge at the bottom, and unless you can get it drained, flushed and refilled/recharged, the only answer is replacement.
 
I come back to my early post, we manufactured special battery charger settings in the late1980's for Westerly, when they used Delco Freedom batteries.

These were about 15.4 volt charge and 14.4 volt float.

You need to get them bench charged at a battery dealer, who knows Delco batteries, then find out there capacity. If they have the delco memory problem, they may only be good for 50 amp hr.

Brian
 
15.4 volts makes more sense, I had 15.6v in my mind. You've not fully charged them at 14.0v, to get a good charge can take up to 72hours not the overnight that seems customary.
 
As others have said, if they are sealed batteries you probably need to take them up to 15V +, say 15.5V before they are charged. Without knowing the characteristics of your charger I can't comment on what is happening at the moment.

For example, if I set my 80A Mastervolt to flooded lead acid float charge it will only ever reach 13.6V and and that would never charge sealed batteries. Take 'em up to 15.5V (or whatever the mfr recommends) and try again.

If they are only three years old, you want to find out how and why they died so soon.
 
I have three 120Amp hours batteries in a bank on the main engine, two used as leisure, one for starting. Having left inverter & fridge on one night in June, the voltage on the two leisure batteries went down to absolutely zero. Wouldn't even power up the simple digital voltmeter wired into the system. Started the engine, charged up for a few hours. A friend came along with a device which did a "load test" which unbelievably showed the leisure batteries as being in good condition. Not believing this, with a holiday about to happen, went and bought two more of the same as standby, and put them on the boat. They are still unused, I had no further problems.
I can't understand what happened, but suggest don't throw the batteries away yet!

IanC
 
I would not disagree with 15.6 volt, it was 20 years ago when I made them, and I was being on the safe side.

My worry is the memory problem the Delco Freedom batteries had, when left partially discharged for a length of time. If these have been left part charged over winter, then they may be only 50 anphour batteries now, or even lower.

The need a proper charge, and then a capacity check, not a high load test.

Brian
 
As the gentleman above said, the correct way of checking is with a hygrometer though that assumes the correct level of acid in the first place. However, battery voltage is a pretty reliable way of doing so, and certainly there is no chance of a battery reading 12.7v only being half charged. It was very near fully charged .

The drop to 10 v shows that the battery is on its last legs. What tends to happen is the lead oxide drops out of the plates reducing the amount there and the capacity of the battery. It forms a sludge on the bottom of the battery case and at some point shorts out the plates causing a totally dead unit. Or thats how I understand it.

The voltage drop would indicate high battery internal resistance not low. The fact that the battery voltage recovered as much as it did suggests that the overall problem is high resistance not that you can do much about it.

Finally, because of internal resistance the basic charging is usually done somewhere in the 14 to 15v range dropping back to 13.5 or thereabouts simply as a float to counter the natural internal discharge of the battery. Incidentally, your charger has to give more than 0.2 amps of it will noit be man enough.
 
But they are sealed so no hydrometer reading, and a differrant construction to leisure / traction batteries, the same rules do not apply.

Brian
 
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As the gentleman above said, the correct way of checking is with a hygrometer though that assumes the correct level of acid in the first place.

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Nigel Calder would disagree with you.

An SG test will tell you if the battery is fully charged BUT only up to its current Ah capacity. If a 105 Ah battery now only has a capacity of 50 Ah because of age/sulphation etc., then the SG test will not show that problem. Taking 12 Ah out of you battery which now has a useably capacity of 25 Ah will take the Ah left down to about 12Ah. This is now at 50% of the useable 25 Ah left, which is why the open circuit voltage recovered to 12.2 volts. 12.2 is half of 12.8, or 12.2 indicates that the battery is down to half its Ah capacity - whatever that might be at the time of the test - not as new!

Beware of hydrometer readings if you can do them - they will tell you if one cell is bad - a load test is much better.
 
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