Batteries, CCA and Amps

[jx2mad]

I know there are threads on here covering this topic but I cannot find an answer to my question. I have a small lead-acid battery rated at 240cca. There is no indication of the amp/hr rating so I cannot work out how long this battery will sustain a load drawing 12A. Any suggestions?

[Mick_Marsh]

I know there are threads on here covering this topic but I cannot find an answer to my question. I have a small lead-acid battery rated at 240cca. There is no indication of the amp/hr rating so I cannot work out how long this battery will sustain a load drawing 12A. Any suggestions?
When fully charged and healthy, your battery is capable of supplying a load drawing 240A. How long for? More information is needed.
What is the make and model no. of your battery?

[bee utey]

Unless the battery is rated for deep cycle use it is unlikely you will find any specifications mentioning amp-hours. Try googling the battery manufacturer. Or buy an ex UPS battery from ebay, there are heaps about.

[101RRS]

There is a rule of thumb for normal starter batteries but I cannot remember it - something like divide the CCA by 10 or 12.

[drivesafe]

Hi Garry and sorry mate but there is no connection between the CCA and Ah of any battery.

The only way you will know the Ah of a battery is if the manufacturer lists it.

For example, and Optima 55 amp deep cycle battery has a CCA of 750 and if you divide the CCA by the Ah, you get a ration of 13.64.

Where as a similar sized Exide cranking battery has an Ah of 50 but only a CCA rating of 400, thats a ration of 8.

As you can see, no comparison and note, even the same cranking size Exide batteries have different Ah.

Hi jx2mad, as posted, you will need to get the exact Ah info from the manufacturer, if they have it available.

[lambrover]

As Drivesafe has said there is no relation between the CCA and AH.


Have a look for a reserve capacity number.

Reserve capacity is the number of minutes a battery can maintain a useful voltage under a 25 ampere discharge. The higher the minute rating, the greater the battery's ability to run lights, pumps, inverters, and electronics for a longer period before recharging is necessary. The 25 Amp. Reserve Capacity Rating is more realistic than Amp-Hour or CCA as a measurement of capacity for deep cycle service. Batteries promoted on their high Cold Cranking Ratings are easy and inexpensive to build. The market is flooded with them, however their Reserve Capacity, Cycle Life (the number of discharges and charges the battery can deliver) and Service life are poor. Reserve Capacity is difficult and costly to engineer into a battery and requires higher quality cell materials.

[PhilipA]

I know there are threads on here covering this topic but I cannot find an answer to my question. I have a small lead-acid battery rated at 240cca. There is no indication of the amp/hr rating so I cannot work out how long this battery will sustain a load drawing 12A. Any suggestions?
Just to try to be helpful I will say that based on a say 440 CCA battery being unlikley to have more than say 40AH, I would guess that a 240CCA battery would be unlikely to run your 12Amp load for more than 2 hours and probably a bit/lot less.
Regards Philip A

[101RRS]

Hi Garry and sorry mate but there is no connection between the CCA and Ah of any battery.



pftttttt :) - party pooper - I read it somewhere so it must be true - is only a rule of thumb so has some inaccuracies.

[drivesafe]

I know there are threads on here covering this topic but I cannot find an answer to my question. I have a small lead-acid battery rated at 240cca. There is no indication of the amp/hr rating so I cannot work out how long this battery will sustain a load drawing 12A. Any suggestions?

Hi jx2mad, I forgot to mention that your battery is probably way too small to maintain a 12 amp load for anything but a few minute without doing some serious harm to your battery.

Maximum CONTINUOS load for any battery should not exceed 10% of the battery’s total Ah ( which you need to determine )or you risk shortening the battery’s life span.

[drivesafe]

I know there are threads on here covering this topic but I cannot find an answer to my question. I have a small lead-acid battery rated at 240cca. There is no indication of the amp/hr rating so I cannot work out how long this battery will sustain a load drawing 12A. Any suggestions?

Hi jx2mad, I forgot to mention that your battery is probably way too small to maintain a 12 amp load for anything but a few minute without doing some serious harm to your battery.

Maximum CONTINUOS load for any battery should not exceed 10% of the battery’s total Ah ( which you need to determine )or you risk shortening the battery’s life span.

[Yorkie]

so is there a way of testing the available ah of a deep cycle battery to see it it is stuffed?
was at batteryworld the other day and bloke tested my 50ah century battery, took a reading with his gadget and divided by 7'ish to give me the available ah and said only 37ah based on the reading??
anyway i can test and calculate using my multimeter at home?

[Blknight.aus]

CCA is how many amps your battery can dump for 30 seconds or a minute (depending on which standard its tested to) while maintaining over 10.5v.


Very very aproximately...

devide CCA by 120 (for the 30 second standard) or 60 (for the minute standard) and that gives you the maximum amps you can draw and have the battery provide power for 60 minutes.

What you really want to look at is the RC (reserve capacity) of the battery, thats how long the battery can put out 20 amps for in minutes and maintain a voltage of over 10.5 or 9.5v (again depending on which standard is used)


you will notice that if you happen to have a battery that clearly explains which standard it was tested to and has both RC and CCA on it that the math on the RC gives a better total AH than the CCA as in

RC(amps*time) > CCA (Amps*time)

its a funky deal with the way that wet cell batteries work and isnt worth stressing about other than to remeber that the less power you draw from the battery the longer it lasts relatively speaking.

[drivesafe]

Hi Dave and not quite right. The industry standard for rating the RC of a battery is set by the amount of time the battery can be discharged at 25 amp ( not 20 ) and the voltage does not drop below 10.5v

The RC is theoretically the amount of time you can operate the average vehicle using a given battery if the alternator fails.

I have no idea how they arrived at the “AVERAGE” vehicle?

Plus, while you can use the RC rating to get a VERY rough idea of a battery’s potential AH, you still have to divid the RC by 2 to get somewhere “near” the battery’s Ah and again, this will vary greatly from one type and make of battery to another.

[Blknight.aus]

ok so that standard is that

SAE, BIC, DIN, IEC, EN, BSR or JIS?

http://www.acdelco.com.au/PDFs/ACDelcoToday_Dec08.pdf

[drivesafe]

Hi Dave and I’ve seen that brochure before.

I must admit to having a good chuckle when I see it. While there is some handy info in it, it is also obvious that it was written by a journalise and not by a genuine battery technician.

For a starter, the brochure goes on about “How batteries loose their power” listing the different devices and how much they might draw.

All good and well but for all the devices to be drawing power, they have to be connected to the battery, again, so far so good.

They then have a chart showing the charge percentage level, specific gravity and the matching voltages for a 12v and 6v battery.

Problem is that they are talking about the current drain caused by devices connected to a battery but the chart is for OPEN CIRCUIT voltage readings.

While a battery has a load on it, no matter how small it is, OPEN CIRCUIT voltage levels are totally irrelevant. Further more, an OPEN CIRCUIT voltage is only accurate after the battery has been sitting in a No-Load/No-Charge state for at least 24 hours.

And while trivial, but just to add insult to injury, every battery shown on that brochure is a sealed type battery, so how do they expect you to get a HYDROMETER reading?

This chart below is for loaded battery voltage readings, but note, to get a reasonably accurate reading with this chart as a reference, the load should be no more than a couple of amps at most.

https://www.aulro.com/afvb/images/imported/2016/06/640.jpg

[Blknight.aus]

the main interesting point of the brochure is that it lists the minimum voltages for the standards... (and those are under load voltages not open circuit)

and batteries are like engines..

which engine do you want the one that makes 150KW or 200HP? (yes thats not a perfect conversion but should serve the point)

Using the fancy battery tester at work I can pass or fail the same n70z by testing 700cca at the SAE or ISO standard.

my point?

The standards aint so standard.

[drivesafe]

The standards aint so standard.

Hi Dave and you’re absolutely correct there and I posted up something I hate seeing others do, I called it the industry “standard” when, in this case, it is not a STANDARD.

What I should have posted is the the 25 amp RC rating is the most commonly used in the industry but this does NOT make it a standard.

Sorry about that, but back to subject and the RC rating is just not suitable for trying to determine the Ah capability of a battery because there can still be as much as a 50% margin of difference between batteries types and makes, so it’s not really suitable to get an idea of Ah.

[Blknight.aus]

yep its getting worse too, Ive seen examples of batteries using different parts of the different standards to get the numbers to look impressive.

and yes there is a simple way of finding out what a battery can provide in terms of RC Ah and CCA (after you pick which one of the standards you want to test to) you plug it in to a multi thousand dollar battery tester and leave it sit for about 20 minutes and it will tell you what your battery is capable of.

you can replicate the testing standard (for RC fully charge the battery then put a 25 amt load in it and see how long it takes do drop below 10.5v)

but theres no seriously reliable way of converting any of the specs to any of the others.

[vnx205]

https://www.aulro.com/afvb/images/imported/2016/06/640.jpg

I thought I would take advantage of the information here and carry out a little experiment to see what voltage was needed to start my 300 Tdi.

The battery is on its last legs and will need to be replaced very soon. If I don't use it for over a week, I am likely to have to top it up with the battery charger. Hardly surprising as the battery is the same one that was in the vehicle when I bought it four and a half years ago.

Anyway after not using the vehicle for five days, I measured the voltage today at 11.5 volts, which according to the table is only about 20% charge. I was a bit surprised that the voltage didn't change perceptibly when I turned on the parking lights. Is that what you would expect? Or don't the parking lights produce enough load to change the voltage?

There was just enough power to allow the glow plugs to operate normally and start the engine, but there wasn't much to spare. It started, but only just.

I realise that running a battery down to 20% is not advisable, but I had hoped that this little experiment would give me some useful information. I thought that if I ever fitted a battery monitor or some sort of volt meter, it would be helpful to know what voltage was needed to start the engine.

Was I wasting my time? Does the figure I came up with of 11.5 being well below what is safe tally with accepted ideas?

[Blknight.aus]

nope for a cranking battery your experiment nicely backs up what the chart provides....

But bare in mind that as you battery is old that your results will be different to a brand new battery.

as an example fozzys old battery (a 3 year old second hand unit donated from big red) wouldnt give enough go to cold start (no glow) the 2.25 if it had anything less than 11v on the gauge in the dash. The new battery however could still cold start the engine with down to about 10.2 (a needle width over the 10v mark) on the gauge. Charging the new battery (same spec different brand) to the magic 13v mark on the gauge took a lot longer on the new battery when it was down low.

[drivesafe]

I thought I would take advantage of the information here and carry out a little experiment to see what voltage was needed to start my 300 Tdi.

The battery is on its last legs and will need to be replaced very soon. If I don't use it for over a week, I am likely to have to top it up with the battery charger. Hardly surprising as the battery is the same one that was in the vehicle when I bought it four and a half years ago.

Anyway after not using the vehicle for five days, I measured the voltage today at 11.5 volts, which according to the table is only about 20% charge. I was a bit surprised that the voltage didn't change perceptibly when I turned on the parking lights. Is that what you would expect? Or don't the parking lights produce enough load to change the voltage?

There was just enough power to allow the glow plugs to operate normally and start the engine, but there wasn't much to spare. It started, but only just.

I realise that running a battery down to 20% is not advisable, but I had hoped that this little experiment would give me some useful information. I thought that if I ever fitted a battery monitor or some sort of volt meter, it would be helpful to know what voltage was needed to start the engine.

Was I wasting my time? Does the figure I came up with of 11.5 being well below what is safe tally with accepted ideas?

Hi vnx205, over the years I have tested many vehicles for how low the battery can be and the vehicle will still start.

Over 20 years ago, when I first started testing while developing the setting for my ( then ) new SC40 battery isolator, I found most vehicles would start from batteries with as low as 11.75 volts ( 30% SoC ) but some older ( thats older even back then ) diesel powered 4x4s, found it hard if not impossible to start with a battery voltage of 11.75v, but all vehicles tested at the time would start with a battery voltage of 12.0v ( 50% SoC ).

By about 2003, all the vehicles I tested had no problems starting off a battery with as low as 11.5v ( about 20% SoC ).

So your findings just confirm what I have come across.

The one thing you didn’t post up is what was the voltage of the battery about 10 hours after you last drove the vehicle and how long was that last drive.

Some clarification of what the voltage reading and State of Charge ( SoC ) of a battery means in relation to the storage capacity of the same battery.

The SoC of a battery relates to the amount of charge in the USEABLE capacity of a battery.

Put another way, if you have a new 100 Ah battery and the SoC voltage is 12.75v, the you have fully charged battery and you have 100 Ah available for use.

If the battery is getting on a bit and some of the battery’s surface is sulphated and only about 80% of the battery’s original capacity is available. If the battery is fully charged it will still have an SoC voltage of 12.75v, this is for the usable 80% of the battery.

The SoC only indicates the charged state of the useable portion of the battery, it does not give you any indication as to just how much of the battery’s original 100 Ah you actually have available.

[vnx205]

Thanks for that explanation. It seems that things are not quite as simple as I thought. So I guess that if a battery was really close to the end of its life, even at about 11.5 volts, if it didn't fire immediately for some reason and had to turn over for a couple of seconds, it might run out of reserve capacity before it started.




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The one thing you didn’t post up is what was the voltage of the battery about 10 hours after you last drove the vehicle and how long was that last drive.

I will try to do a test to get that figure, but I may replace the battery before I get a chance.

Some clarification of what the voltage reading and State of Charge ( SoC ) of a battery means in relation to the storage capacity of the same battery.

The SoC of a battery relates to the amount of charge in the USEABLE capacity of a battery.

Put another way, if you have a new 100 Ah battery and the SoC voltage is 12.75v, the you have fully charged battery and you have 100 Ah available for use.

If the battery is getting on a bit and some of the battery’s surface is sulphated and only about 80% of the battery’s original capacity is available. If the battery is fully charged it will still have an SoC voltage of 12.75v, this is for the usable 80% of the battery.

The SoC only indicates the charged state of the useable portion of the battery, it does not give you any indication as to just how much of the battery’s original 100 Ah you actually have available.

Would it be a fair comparison to say that having a fully charged new battery is a bit like having a big water tank on a tall tank stand; quite a bit of pressure (voltage) and quite a bit of water (reserve capacity)?
An old battery is a bit like having a smaller water tank on a shorter stand; less pressure and less capacity. Even if you raise the stand to increase the pressure (charge the battery to get the voltage up), it runs out of water pretty quickly.

[drivesafe]

Hi vnx205, thats close but to use your tank comparison.

It would be like having two tanks side by side at the same high from the ground. One new and one old.

The new one is full of water but the old one has accumulated a fair bit of sediment.

Both tanks will have the same pressure ( voltage ) when they are full but the older tank runs out of water sooner.

The more sediment, the less the older tank holds but it will still have the same pressure ( voltage ) when it’s full.