Deceased battery

[Chrisc]

Hopefully someone can advise me if my 85ah deep cycle battery is kaput.
I charged it on a 3 stage charger. When disconnected from the charger it was at 13.6v. I then let it sit for 12 hours, at which point it was at 12.6v. A 55 watt bulb was then connected and left for 15 hours. After disconnecting I let it sit for 4 hours, at which point it was at 11.75v. By my calculations, if the battery is good then it should have about 20℅ charge remaining and be at 12v. Is this correct?
Is it time for a new battery?

[sabray]

You are cycling the batt way beyond its norm. Just discharging this small batt as deep as you did is killing it. No mention of batt type. Or charge regiment. It was probably beyond premium condition and then you burned it down beyond its regular cycle one more time. Check the charge suggestion from the manufacturer .
That's a small bat for a deep cycle load.,

[deckofficer]

You got 69 a-hr out of it. Remember it got its 85 a-hr rating in a 20 hour test pulling 4.25 amps. I would say it is in good shape.

[Chrisc]

It is (or was:-) a flooded battery.
I was advised that it would stand a deep discharge provided that it was recharged promptly by a calcium charger, before sulphation could cause serious damage. The battery is coming up 5 years old so is probably getting a bit senile and due for retirement anyway, although even at less than peak performance it is still more that sufficient for us on a 30 foot yacht in which we cruise for months at a time - oh, the joys of keeping your boat electrically simple!
I guess what I wanted to know by my test was the current status of the battery.

[sabray]

At about 12.2 volts your 50 percent discharged depending on bat type. Going below that diminishes most batts. Means they don't recover or hold as well. Lots of deep cycles that deep hurts performance . Cheap lead acid won't do well going that deep with repetion. Maybe you could boil it with over charge and blow off the plates..

[Stu Jackson]

And you did this why?

[Chrisc]

I should have been a little clearer.
Under normal usage, we never discharge our little battery below 12.3v. Of late, I have noticed that the battery is a little reluctant to come up to full charge - 12.6v at rest. The deep discharge, ie taking the battery down to 20% capacity over 75% of the standard 20 hour discharge rating is a means of testing a deep cycle battery. I should say that in this I am passing on what I have been told, not what I know as fact.

[noelex 77]

I think your calculations are roughly correct.
To do this accurately you really need to measure the current over time. 55w bulbs are rarely accurately 55w and car bulbs are often rated with a voltage of 13.8v.

If we assume the 55w was accurate and the average discharge voltage was 12.3v. The current was 4.47 A over 15 hours that is 67AHrs was drawn from your battery. This was at C19,
We need to rember the 85AHrs was claimed with a brand new battery 100% charged (it takes a long time to get to this level) and at C20, or possibly C25, or even C100. The termination voltage is very low usually 10.5v.
Would your battery have delivered another 20% or another 18AHrs if you had continued the test down to 10.5v. Probably not, but would have come close.

When using the resting voltage of 11.75v to estimate SOC you need to let the battery rest longer than 4hours (24 or even 48hours). The voltage then needs to be compensated for temperature.

In short I think your battery did fine. Certainly within the limits of your experimental design and remembering that the full 85AHrs is difficult to get.

[noelex 77]

Originally Posted by Stu Jackson

And you did this why?

A capacity test like this is not so stupid. Nigel Calder recommends doing one every 12months if my memory serves me correctly.
The test is hard on the batteries and I don't agree with doing this as a routine that frequently, but it is a tool that should be used a bit more often to answer battery questions.

It is worth doing if you go are going to throw any batteries out. It is also worth doing if crusing to areas where batteries may be hard, inconvenient, or expensive to get, or as in this case, when you suspect your batteries are dying, but are not sure. It is very important to immediately charge your batteries up at the termination of the test.

More accurate results can be had if you monitor the acual current used (or use a battery monitor to count the AHrs)

[Maine Sail]

Originally Posted by noelex 77

A capacity test like this is not so stupid. Nigel Calder recommends doing one every 12months if my memory serves me correctly.
The test is hard on the batteries and I don't agree with doing this as a routine that frequently, but it is a tool that should be used a bit more often to answer battery questions.

It is worth doing if you go are going to throw any batteries out. It is also worth doing if crusing to areas where batteries may be hard, inconvenient, or expensive to get, or as in this case, when you suspect your batteries are dying, but are not sure. It is very important to immediately charge your batteries up at the termination of the test.

More accurate results can be had if you monitor the acual current used (or use a battery monitor to count the AHrs)

According to the guys at Lifeline/Concord battery aircraft batteries are required to undergo capacity testing. The machines they sell to do this run into the multiple thousands of dollars.. I have a capacity tester and provided you immediately re-charge very little ill effects will come of it. Lifeline and Odyssey also have a "reforming" charge protocol that I have used successfully that most would claim will destroy the batts yet it actually works really well.

The only way to know true capacity is to physically measure it with a reserve capacity or 20 hour load test... The old bank from our boat has been 20 hour load tested 5 times to 10.5V and they are now going into their 8th season.. They still have about 92-93% of new capacity.. At a charge rate of 20% of "c" from 50% SOC they remain in bulk for 102 minutes which means they are in very good health for the age. This despite capacity tests to 10.5V....

[noelex 77]

Originally Posted by Maine Sail

I have a capacity tester and provided you immediately re-charge very little ill effects will come of it.

You have all the best toys

The good thing about a capacity test is it can be done with minimal equipment with a bit of care, by the average boat owner. It tells you a lot about the heath of a deep cycle battery. Indeed it is directly measuring what we are interested in. How much capacity has this battery got.

One point that has not been mentioned is that it better done on each battery separately rather than the bank as a whole.

[Maine Sail]

Originally Posted by noelex 77

You have all the best toys

The good thing about a capacity test is it can be done with minimal equipment with a bit of care, by the average boat owner. It tells you a lot about the heath of a deep cycle battery. Indeed it is directly measuring what we are interested in. How much capacity has this battery got.

One point that has not been mentioned is that it better done on each battery separately rather than the bank as a whole.

The first one I built used a battery monitor and a relay to cut the load at 10.5V.. The biggest problem is with accuracy and holding the load constant as the voltage drops... A 5A load on a 100Ah battery does not remain constant at 5A, as it should, to get the most accuracy. A tester like this requires human intervention to maintain the load as a constant...

You are 100% correct that each battery needs to be tested individually...

[Dockhead]

Originally Posted by Maine Sail

The first one I built used a battery monitor and a relay to cut the load at 10.5V.. The biggest problem is with accuracy and holding the load constant as the voltage drops... A 5A load on a 100Ah battery does not remain constant at 5A, as it should, to get the most accuracy. A tester like this requires human intervention to maintain the load as a constant...

You are 100% correct that each battery needs to be tested individually...

So, in sum, it seems like the OP's test was methodologically sound, and not harmful if he recharged immediately, notwithstanding expressions of doubt earlier in the thread. Sounds like your batts are doing great for their age, and will give you some more years of service.

Actually, I think I read somewhere that running out a sulfated battery dead flat and then recharging it can help revive it. So perhaps such a test might even be beneficial for old batts?

I use an Argus pulse tester to track the health of my batts. This is a nice toy, although I cannot say for sure whether it is as accurate as a real deep discharge test, although for sure it's a lot faster and easier.

Mine are going strong after two years of hard use with no shore power, despite being run out dead and left like that for weeks, on two different occasions. Maybe lead-acid batts aren't so horrible as we sometimes think.

[Maine Sail]

Originally Posted by Dockhead

So, in sum, it seems like the OP's test was methodologically sound, and not harmful if he recharged immediately, notwithstanding expressions of doubt earlier in the thread. Sounds like your batts are doing great for their age, and will give you some more years of service.

Actually, I think I read somewhere that running out a sulfated battery dead flat and then recharging it can help revive it. So perhaps such a test might even be beneficial for old batts?

I use an Argus pulse tester to track the health of my batts. This is a nice toy, although I cannot say for sure whether it is as accurate as a real deep discharge test, although for sure it's a lot faster and easier.

Mine are going strong after two years of hard use with no shore power, despite being run out dead and left like that for weeks, on two different occasions. Maybe lead-acid batts aren't so horrible as we sometimes think.

I own both an Argus 500 and a Midtronics EXP-1000 HD. They are both in darn close agreement. Why?

Argus stole proprietary information from Midronics and then lost the court battle thus putting them out of business.

I like my Argus because it will actually tell me internal resistance, which my significantly more expensive Midtronics will not. These are both great tools IF you get an "as new" baseline and then follow it. If you don't have a baseline to work from they are an okay rough guide..

They do not however translate very well to an actual capacity test. I find that when a battery reads about 85% of new on the Argus it is ready to be replaced.

[Dockhead]

Originally Posted by Maine Sail

I own both an Argus 500 and a Midtronics EXP-1000 HD. They are both in darn close agreement. Why?

Argus stole proprietary information from Midronics and then lost the court battle thus putting them out of business.

I like my Argus because it will actually tell me internal resistance, which my significantly more expensive Midtronics will not. These are both great tools IF you get an "as new" baseline and then follow it. If you don't have a baseline to work from they are an okay rough guide..

They do not however translate very well to an actual capacity test. I find that when a battery reads about 85% of new on the Argus it is ready to be replaced.

Yes, I took a baseline with the Argus when the batts were new, and keep a log since. I pay no attention to the "% New" reading which seems to me useless as the "% charge remaining" reading on battery monitors. I compare the actual numbers, and I'm actually more interested in the relative numbers than the absolute. Likewise with specific gravity readings, which I also log.