Battery condition

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NigelCraig

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Is 13.4V Ok for a 12volt battery? Best I could achieve after about 6 hours on an ordinary cheap auto type trickle charger.
 
NigelCraig said:
Is 13.4V Ok for a 12volt battery? Best I could achieve after about 6 hours on an ordinary cheap auto type trickle charger.
Click to expand...

On charge ? no to low

Off charge, let it settle for 6 hours, looking for around 12.8 volt, but may have surface charge, not deep charge thus small capacity.

Brian
 
Nigel

Thanks - unreadable so removed it! I'll try again - should be able to get it on the web but can't find the link at present!

EDIT

Here goes - I use this little table as a guide to the state of charge of conventional flooded lead acid batteries. I cannot recall the web source, but you will find many such tables - but most are simpler, and do not give the voltage for different current draws.

State Of Charge (%) versus Voltage for various battery conditions

SOC (%) 100 90 80 70 60 50 40 30 20 10 0
V, Rested 12.8 12.7 12.6 12.5 12.4 12.3 12.2 12.1 12.0 11.9 11.8
V, at 0A 12.5 12.4 12.3 12.2 12.1 12.0 11.0 11.8 11.7 11.6 11.5
V, at 5A 12.4 12.3 12.2 12.1 12.0 11.9 11.8 11.7 11.6
V, at 10A 12.2 12.1 12.0 11.9 11.8 11.7 11.6 11.5

Sorry - even using spaces instead of a table does not work! To reconstruct the table, just bear in mind the last two rows have no values for the last two and three columns respectively. I'll go away and learn about Photobucket.
 
Last edited:
Hydrozoan said:
Nigel

Thanks - unreadable so removed it! I'll try again - should be able to get it on the web but can't find the link at present!
Click to expand...

The values are about right, remember though that temperature can alter them, 0.05 volt / 20 degree F, dropping as temperature rises. The 5 A and 10A voltage readings varies on battery bank size, the values given is about 5 and 10% of battery bank size, i.e. based on 100 amp hour capacity.

Brian
 
Brian - thanks for that. Yes, my batteries are each about 100Ah and I find it a useful little table, having just a voltmeter switchable to the different batteries, not a full-blown "state of charge" meter.
 
halcyon said:
On charge ? no to low

Off charge, let it settle for 6 hours, looking for around 12.8 volt, but may have surface charge, not deep charge thus small capacity.

Brian
Click to expand...

Reading taken with voltmeter immediately after disconnecting charger (which spent most of time connected in maintenance mode). I think if I leave them (3 x Numax CXV24 86ah sealed) for a time but without doing anything to discharge them and without charger connected, drops back to 12.3-12.4. Probably need a drop test.
 
Hydrozoan said:
I'll go away and learn about Photobucket.
Click to expand...

In the meantime:

BatterySoC_zps6d1f7ed5.png~original


Also, .ZIP file of Excel spreadsheet attached.
 

Attachments

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rivonia said:
Sorry to but in BUT...11.8 IS NOT FULLY DISCHARGED. I am not alone on here when I say that a battery down to as low as 10V can be fully recovered. I know this as that is what I have done.

Over to the experts

Peter
Click to expand...

It has no usable capacity below 11.8 rested voltage, put a load on and the voltage drops nearly vertically, come to it 12.8 is not necessarily a fully charged battery.

Brian
 
Some AGM batteries have a fully charged specific gravity of 1.300. This will give you an OCV at 25 degrees of 12.9-13V.
Truck/leisure batteries are usually about 1.260 giving an OCV of about 12.7V.
Some heavy duty industrial batteries are as low as 1.220 giving an OCV of about 12.4-12.5V.
There's quite a range, and of course it is temperature dependent too.

Whether a lead acid battery is fully discharged is a matter of definition. It's a chemical process occurring more and more slowly as the active materials deplete so in theory you will only approach it asymptotically. In practise you do not run it to exhaustion of any of the active materials.

In wet batteries there is a surplus of electrolyte and a surplus of negative plate capacity, but normally the positive plates will be pretty fully converted to lead sulphate by the time the s.g. is down to 1.100 giving an OCV of around 11.7V. It is really not a good idea to go below that! Really deeply discharged plates are harder to recharge.

In AGM and gel batteries there is a near stoichiometric quantity of acid or even a deficit, so if you over-discharge you can get it virtually to 1.000 i.e. water. If you do this the battery is very difficult or impossible to recharge. There is in these batteries a surplus of positive plate capacity, but the negatives will be pretty fully converted by the time the s.g. is down to 1.100.

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.

Alright Peter?
 
Georgio said:
can you explain "V, at 0A" does that mean " battery has been discharged a bit but the load removed and battery not rested"? Sorry if I'm being thick I can understand the rest of it.
Click to expand...

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.

Since it is difficult to rest the battery for, say, 4 hours or more when on board, I think it is useful to have the V at 0A values - if one used the rested values instead, they would indicate a substantially lower residual charge. But I must stress that I use the table as a rough guide only - and as halcyon pointed out above, the values are temperature dependent, and the V at 5 and 10A figures are for a battery of about 100Ah.
 
Georgio said:
can you explain "V, at 0A" does that mean " battery has been discharged a bit but the load removed and battery not rested"? Sorry if I'm being thick I can understand the rest of it.
Click to expand...

No it means open circuit voltage after a decent period of rest after a bit of a discharge, or after prolonged storage. (It won't change much after a low load but it matters at high load.)
The open circuit voltage will give a reasonable idea of the state of charge of a healthy battery.
What it will NOT do is tell you whether a battery is healthy and capable of delivering its nominal capacity.
 
Troubadour said:
Some AGM batteries have a fully charged specific gravity of 1.300. This will give you an OCV at 25 degrees of 12.9-13V.
Truck/leisure batteries are usually about 1.260 giving an OCV of about 12.7V.
Some heavy duty industrial batteries are as low as 1.220 giving an OCV of about 12.4-12.5V.
There's quite a range, and of course it is temperature dependent too.

Whether a lead acid battery is fully discharged is a matter of definition. It's a chemical process occurring more and more slowly as the active materials deplete so in theory you will only approach it asymptotically. In practise you do not run it to exhaustion of any of the active materials.

In wet batteries there is a surplus of electrolyte and a surplus of negative plate capacity, but normally the positive plates will be pretty fully converted to lead sulphate by the time the s.g. is down to 1.100 giving an OCV of around 11.7V. It is really not a good idea to go below that! Really deeply discharged plates are harder to recharge.

In AGM and gel batteries there is a near stoichiometric quantity of acid or even a deficit, so if you over-discharge you can get it virtually to 1.000 i.e. water. If you do this the battery is very difficult or impossible to recharge. There is in these batteries a surplus of positive plate capacity, but the negatives will be pretty fully converted by the time the s.g. is down to 1.100.

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.

Alright Peter?
Click to expand...

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?
 
Troubadour said:
No it means open circuit voltage after a decent period of rest after a bit of a discharge, or after prolonged storage. (It won't change much after a low load but it matters at high load.)
The open circuit voltage will give a reasonable idea of the state of charge of a healthy battery.
What it will NOT do is tell you whether a battery is healthy and capable of delivering its nominal capacity.
Click to expand...

What is 'a decent period of rest' and 'a bit of discharge? Would not 'prolonged storage' result in a 'rested' condition?

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?

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.

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.
 
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.
 
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