Battery condition

[Plevier]

See comments below.

What is 'a decent period of rest' and 'a bit of discharge? Would not 'prolonged storage' result in a 'rested' condition?
## I meant open circuit voltage either after prolonged storage, or after a rest period following a partial discharge. In other words, not immediately after supplying a load. I hope that is clearer.

I have read that battery manufacturers cite 24 hours for the fully 'rested' condition, but have also seen a references to 4-6 hours for a reasonable approach to rested condition, so V at 0A is presumably for a period less than that?
## There's no exact answer. You might need as much as 24 hours after very vigorous charging. 4-6 hours would be more typical.

I had also assumed that a very high prior load, relative to battery Ah, could distort subsequent V at 0A, but that (for a 100Ah battery, say) a period at 5A or 10A discharge would not.
## I would agree a 10% load won't have a lot of effect. However you are looking at pretty small voltage variations here so wise to give some recovery time. Probably 30 mins would do.

No, voltage measurements alone cannot reveal a battery which has lost substantial capacity, I accept. For that, see posts 2 and 3. As I say, I just use the table as a rough guide, assuming batteries in good condition.
## Fine, but don't expect great accuracy.

 

[Plevier]

No not allright.

I had batteries x 7 all 100amp sealed lead acid. Two of them slowly discharged down to 10.8V. I disconnected them and charged them seperately this took over 24 hours. By then both were up to 14.2 volts and so were fully charged. The resting charge after a further 24 hrs was 13.2 back to the battery bank and connected. All working perfectly normal.

What say you?

Not a lot. I don't see any conflict with what I said. I was explaining not contradicting.
(Quote - So for all 12V lead acid batteries, it's wise to consider something like 11.8V as fully discharged, even though that doesn't mean you have converted all the active material and taken the chemical reaction to completion.)
You deep discharged the batteries, you got away with it. I didn't say they would self destruct first time.
Won't do them any good though!

 

[halcyon]

I also wondered what the 0A row meant, and came to the conclusion it was an expected reading while the battery was in use, but the load had just disconnected.

I would also prefer that the rows below said 5% and 10% rather than 5A and 10A. Probably best to use the spreadsheet and substitute with values from your capacity.

The 0A is a confusion, though is there, is only relevant for a point in time as the voltage is rising from the 0A to rested constantly.

All the voltages are only a guide, actual voltage will vary with temp, age, how the batteries are charged, how they are used, how they are maintained, air pressure and so on. The open circuit voltage of a new battery increases during initial use, fully charged can be over 13 volt, falling in time to around 12.8 volt fully charged.

The figure gives a good working guide, say + or - 5%, after all how much of a problem is 60 - 70 % as a battery capacity ? we say re-charge at 50% capacity, charging at 45 or 55% is not going to kill the battery.

Don't try and read to much into values.

Brian

 

[ghostlymoron]

Well said Brian. It's all about digitalitis (putting absolute faith in digital information).

 

[sailinglegend420]

...I had batteries x 7 all 100amp sealed lead acid. Two of them slowly discharged down to 10.8V.

10.8 volts under a small load and then allowed to rest will probably get back to 11.7v. The "off load", "off charge" voltage is the important one.

....I disconnected them and charged them seperately this took over 24 hours. By then both were up to 14.2 volts and so were fully charged.....

Slightly misleading for some people! When batteries first get back to 14.2 volts they are at about 80% charged - leave each one for 24 hours and it should be back to 100%, although a voltage of 14.2v may not be high enough to cause the slight gassing batteries need to charge properly and stir up the electrolyte (FLA about 14.4v, depending on temperature) A multi-stage charger is the only way to properly charge a deep cycle batteries and extend their life cycle.

 

[JeannetteAbbott]

That is pretty high i guess.

 

[Plevier]

10.8 volts under a small load and then allowed to rest will probably get back to 11.7v. The "off load", "off charge" voltage is the important one.


Slightly misleading for some people! When batteries first get back to 14.2 volts they are at about 80% charged - leave each one for 24 hours and it should be back to 100%, although a voltage of 14.2v may not be high enough to cause the slight gassing batteries need to charge properly and stir up the electrolyte (FLA about 14.4v, depending on temperature) A multi-stage charger is the only way to properly charge a deep cycle batteries and extend their life cycle.

Yes all true.
I missed the point that Peter possibly meant 10.8V under load not open circuit. Big difference. Even so 10.8V is very low to go under a small load.

 

[Plevier]

All the voltages are only a guide, actual voltage will vary with temp, age, how the batteries are charged, how they are used, how they are maintained, air pressure and so on. The open circuit voltage of a new battery increases during initial use, fully charged can be over 13 volt, falling in time to around 12.8 volt fully charged.

The figure gives a good working guide, say + or - 5%, after all how much of a problem is 60 - 70 % as a battery capacity ? we say re-charge at 50% capacity, charging at 45 or 55% is not going to kill the battery.

Don't try and read to much into values.

Brian

+1

 

[Hydrozoan]

Thanks to Troubador and halcyon for responding to the request for elaboration - and to repeat their emphasis, I use the table as no more than a rough guide. (BTW, I am mortified to have lost its source - though it was about 10 years ago! - and so was pleased that halcyon confirmed that the figures are about right.)

Regarding the discussions of Rivonia's observations, I am reminded of the dead parrot sketch in Monty Python. A battery taken down once to 10.8V will certainly be 'stunned', but will not necessarily be an 'ex-battery' that has 'ceased to be'. But more of that treatment and its 'metabolic processes' will soon be ''istory'.

 

[sailinglegend420]

..... so 10.8V is very low to go under a small load.

I let one of my 10 year old AGMs go down to 10.8 volts when I disconnected the positive cables of all the batteries to do some load testing and one of the batteries touched a through-hull fitting!!!! I don't know for how many days? I should have disconnected the negatives, as I keep telling everybody, but in this case the positives were easier as the cables were marked up.The dead battery charged up OK and when I ran the 10 hour test again it performed better than the other batteries!!!!!!!

 

[Richard10002]

I let one of my 10 year old AGMs go down to 10.8 volts when I disconnected the positive cables of all the batteries to do some load testing and one of the batteries touched a through-hull fitting!!!! I don't know for how many days? I should have disconnected the negatives, as I keep telling everybody, but in this case the positives were easier as the cables were marked up.The dead battery charged up OK and when I ran the 10 hour test again it performed better than the other batteries!!!!!!!

What is your ten hour test, and how do you do it?

 

[ghostlymoron]

This seems a good way to determine battery capacity.
http://www.instructables.com/id/AmpHourTest/?ALLSTEPS

 

[Plevier]

Regarding the discussions of Rivonia's observations, I am reminded of the dead parrot sketch in Monty Python. A battery taken down once to 10.8V will certainly be 'stunned', but will not necessarily be an 'ex-battery' that has 'ceased to be'. But more of that treatment and its 'metabolic processes' will soon be ''istory'.

Excellent!
:applause:

 

[Plevier]

I let one of my 10 year old AGMs go down to 10.8 volts when I disconnected the positive cables of all the batteries to do some load testing and one of the batteries touched a through-hull fitting!!!! I don't know for how many days? I should have disconnected the negatives, as I keep telling everybody, but in this case the positives were easier as the cables were marked up.The dead battery charged up OK and when I ran the 10 hour test again it performed better than the other batteries!!!!!!!

An Italian Tune Up for your favourite L******e batteries
Bet you aren't going to do it again though.

 

[sailinglegend420]

What is your ten hour test, and how do you do it?

I was trying to get an idea of the capacity left in my 10 year old Lifeline AGMs. The proper way is to discharge with a constant current (keep turning on more lights as the voltage goes down) at the 20 hour rating of the battery. This is the load the battery is designed to take for 20 hours before it goes flat. So for a 210Ah batteries' 20 hour rating the load should be 210/20 = 10.5 amps. Keep this constant load on till the battery gets to 10.5 volts and note the time. If it took 20 hours the capacity was at 210 Ah when the test was started. If it only took 10 hours to fall to 10.5v then I assume the battery capacity had started at only 50% of its original capacity, so it has taken only 105Ah to flatten it.
EDIT: This is probably not correct as the 20 hour load test for a 105Ah battery should have been 5.25 amps, it would then last the whole 20 hour test before falling to 10.5v.

The problem with this test is maintaining the constant current for 20 hours without an automatic load device. So a 10 hour test SEEMS an easier test to do, but it is not as accurate as the battery gives out more power at the lower voltages, especially when it gets old. Also fully discharging a battery doesn't seem like a good idea, but others have said that occasionally this is good for it.

If you plot the voltages every hour on a graph for each battery you can get a very good idea of how they are doing, and maybe identify one that is starting to fail. If you can then equalize them first before the test. Alternatively do the test first then equalize, and repeat the test to see the difference equalization has made.

Just as a side issue a "load tester" is no way to test the remaining capacity of a deep cycle battery. It may tell you if it is dead, it may pass the test, but won't give any idea of the capacity left.

 

[catlotion]

Well if you're being thick then so am I , as I have understood it to mean that. I have also assumed that for practical purposes the V at 0A values depend only on the state of charge, and not otherwise on the magnitude and duration of the previous load. But I am not a battery expert so perhaps one will elaborate.

I'd also like a bit of clarification/help please. I'd like to ascertain the effectiveness of a recently installed 80w solar panel on our 2 x 110AH bank. In the absence of a proper battery monitor can I assume that a voltage measurement taken when I return to the boat after a couple of weeks will be 'rested' according to that table (assuming that the solar panel regulator has stopped the panels charging the batteries)?

Also, if we use the boat during a weekend (loading the batteries with heater, fridge, etc) is there any way to ascertain the state of charge at the end of the weekend with nothing more than a multi-meter?

thanks!

 

[Hydrozoan]

In the absence of a proper battery monitor can I assume that a voltage measurement taken when I return to the boat after a couple of weeks will be 'rested' according to that table (assuming that the solar panel regulator has stopped the panels charging the batteries)?

Also, if we use the boat during a weekend (loading the batteries with heater, fridge, etc) is there any way to ascertain the state of charge at the end of the weekend with nothing more than a multi-meter?

Assuming no charging OR discharging, I would regard that as 'rested'. As to your 'end of weekend' question, as discussed in the above posts using simple voltage readings will not, even if the battery is in good condition, give you a very accurate estimate of state of charge. Measuring the specific gravity of the battery acid can give a much more accurate estimate, but obviously is not possible with sealed, AGM or gel types - and is more trouble to do. If it is really critical, you will need a specialised meter which relies on computer modelling of the battery, but as I have no experience of such I will leave someone else to advise you about them.

 

[rivonia]

Not a lot. I don't see any conflict with what I said. I was explaining not contradicting.
(Quote - So for all 12V lead acid batteries, it's wise to consider something like 11.8V as fully discharged, even though that doesn't mean you have converted all the active material and taken the chemical reaction to completion.)
You deep discharged the batteries, you got away with it. I didn't say they would self destruct first time.
Won't do them any good though!

Thanks for the input-agree with you

Peter

 

[sailinglegend420]

.... can I assume that a voltage measurement taken when I return to the boat after a couple of weeks will be 'rested'.

No!

You have to disconnect the negative connector from the batteries so that no charge or discharge is happening. There may be a load from a bilge pump switch, a car radio memory, a Navtex, or phone chargers or even a light left on in the engine room!!! The Solar Panel may be sitting at a float voltage of 13.2v or more, even when the sun is not shinning.

..... if we use the boat during a weekend (loading the batteries with heater, fridge, etc) is there any way to ascertain the state of charge at the end of the weekend with nothing more than a multi-meter?

No. You would have to disconnect the battery, wait for 6 hours and then refer to the table above. This table does not apply to all types of battery.

Get a good battery monitor and install it properly, switch off the auto-sync feature and do it manually when YOU know the batteries are fully charged, or get yourself a SmartGauge battery monitor which is so easy to install because it only measures voltage. It uses clever algorithms and measures the rise and fall of the voltage 1100 times a second and is far more accurate than a shunt current measuring battery monitor, especially as batteries age. I have both on board.

 

[catlotion]

No!

You have to disconnect the negative connector from the batteries so that no charge or discharge is happening. There may be a load from a bilge pump switch, a car radio memory, a Navtex, or phone chargers or even a light left on in the engine room!!! The Solar Panel may be sitting at a float voltage of 13.2v or more, even when the sun is not shinning.

forgot to mention that batteries are isolated. Nothing is left on. Take your point on the solar panel float voltage though.

Get a good battery monitor and install it properly, switch off the auto-sync feature and do it manually when YOU know the batteries are fully charged, or get yourself a SmartGauge battery monitor which is so easy to install because it only measures voltage. It uses clever algorithms and measures the rise and fall of the voltage 1100 times a second and is far more accurate than a shunt current measuring battery monitor, especially as batteries age. I have both on board.

yep - it's on the list (with so many other things) - I just wanted to get an idea of how the panels are performing when we next visit...