Thread: Battery problem, battery testing and CCA vs RC

Did they use a carbon pile tester?

We have the "clever" digital one, it seems pretty accurate, but we always use the carbon pile tester if we suspect the digital one is lying, as that is the only true way to load the battery like the engine does.

I'd probably charge and then unhook the battery to leave it for a similar period to the one that was leaving it flat in the car, and then try starting the car with it.

The test you are doing is the other one I would suggest, it's a good idea.

Hi POD and from what you have posted, my guess is your battery is badly Sulphated.

If it is then this behold account for the short term discharging.

NOTE your battery can be badly Sulphated, which means your capacity is down.

ALSO NOTE a load test has nothing todo with a battery’s capacity, it is only intended toes if the battery can deliver the CCA required, a the CCA has nothing to do with a battery’s capacity.

Furthermore, you can not use a battery’s CCA reading to determine it capacity.

You can have a battery go flat over night, charge it enough to start your motor and then drive to where ever you are getting it tested. The short trip to the tester will supply enough SURFACE charge to get a decent CCA reading.

The one thing a CCA test will do is confirm the battery is not stuffed if it returns a GOOD CCA reading.

The Discharge test you are carrying out right now is by far the best way to find a battery’s accrual capacity.

BUT you do not have to discharge it to 0% capacity, just discharging to 12.0v as this is about 50% capacity. You can do your math from there a see if the battery is down on capacity.

If you find the battery is down on capacity, try these two links for a fix.


Scroll down the page till you get to “LOAD TEST”
https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-10.html


Scroll down the page till you get to “Battery Maintenance”
https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-8.html

Originally Posted by drivesafe

Hi POD and from what you have posted, my guess is your battery is badly Sulphated.

If it is then this behold account for the short term discharging.

NOTE your battery can be badly Sulphated, which means your capacity is down.

ALSO NOTE a load test has nothing todo with a battery’s capacity, it is only intended toes if the battery can deliver the CCA required, a the CCA has nothing to do with a battery’s capacity.

Furthermore, you can not use a battery’s CCA reading to determine it capacity.

You can have a battery go flat over night, charge it enough to start your motor and then drive to where ever you are getting it tested. The short trip to the tester will supply enough SURFACE charge to get a decent CCA reading.

The one thing a CCA test will do is confirm the battery is not stuffed if it returns a GOOD CCA reading.

The Discharge test you are carrying out right now is by far the best way to find a battery’s accrual capacity.

BUT you do not have to discharge it to 0% capacity, just discharging to 12.0v as this is about 50% capacity. You can do your math from there a see if the battery is down on capacity.

If you find the battery is down on capacity, try these two links for a fix.


Scroll down the page till you get to “LOAD TEST”
https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-10.html


Scroll down the page till you get to “Battery Maintenance”
https://www.aulro.com/afvb/the-verandah/246755-line-auto-electrical-info-8.html

Thanks for that info, it is exactly what I suspected, i.e. that the test the shopkeeper performed is unrelated to the complaint that I have. One significant question that remains though- is the deterioration in the capacity of the battery a warranty issue? I recognise that my driving pattern is very hard on a battery, but that's what a warranty is for isn't it?
The bench test in is it's early stages but I just checked and after 5 hours with a 480ma load, the battery has so far gone from 13.1 to 12.9 volts.

Originally Posted by shack

Did they use a carbon pile tester?

We have the "clever" digital one, it seems pretty accurate, but we always use the carbon pile tester if we suspect the digital one is lying, as that is the only true way to load the battery like the engine does.

I'd probably charge and then unhook the battery to leave it for a similar period to the one that was leaving it flat in the car, and then try starting the car with it.

The test you are doing is the other one I would suggest, it's a good idea.

I don't know what sort of tester, except that it had analogue needle readout. Still, as above, I think the load test is irrelevant to the problem I'm experiencing.

I've had a 480mA load on the battery and it is now down to 12.009V as of 9am today, 69 hours (4,140 minutes) in. My calculations, extrapolating from the 50% discharge and dividing the minutes by 52 (480mA is 1/52 of 25amps) suggest that this equates to a Reserve Capacity (RC) of 159.23 (159.23 minutes to full discharge at 25 amps). The label on the battery gives RC as 160.

This suggests that the battery capacity is pretty much what it should be, which suggests that my problem lies elsewhere in the vehicle and that I need to repeat my test for parasitic drain.


Please chime in if I've got this wrong.

Hi POD and sorry mate, if it was only that simple.

Never is!

To carryout a test to the RC standards, the load applied to a battery, any sized battery, must be a constant 25amps during the discharge cycle.

While your math is OK, unfortunately it can not be used to determine the capacity in a LEAD ACID battery.


NOTE, it would work perfectly for LITHIUM batteries.


There’s a storage phenomenon where a lead acid battery, be it a wet cell or an AGM, has a decreased capacity as the discharge current load is increased.

The relation between the discharge current applied to a battery compared to the capacity of that battery can be calculated using Peukert’s Law or Peukert’s Exponent.

Trust me. the calculations are long and involved.

But basically if you apply a 1 amp load to a 100Ah battery, it should take around 150 hours to drain the battery.

If you apply a 5 amp load to a 100Ah battery ( C20 rating ) it should take around 20 hours to drain the battery

If you apply a 10 amp load to a 100Ah battery, it should take around 7 hours to drain the battery.

As you can see, there is no NORMAL math that would give you those sorts of results.


Now taking into a VERY rough account of Peukert’s Law, your 160Ah battery is way WAY under capacity.

Thanks for that info Drivesafe, curiouser and curiouser...
From what I have read over the last couple of days, the Residual Capacity of 160 represents the number of minutes to discharge the battery with a constant 25a load; I guess I need to set up a 25a load and see what it does then?

Brings me back to the same question though; if the battery is sulfated such that the capacity is significantly decreased, would this be a warranty matter (battery is halfway through the warranty period); i.e. should I be pursuing a warranty claim on this battery, or attempting to reclaim the lost capacity myself by applying the advice from your linked article?

One of the tasks on my list over the next few days is to set up a solar panel battery maintainer for this car. Seems it is only going to continue to be a problem otherwise.

Hi again POD, the Ah rating of all lead acid batteries ( regardless of size ) is based on a C20 test.

This is what the manufacturer states their battery will provide in a 20 hour discharge using a current load that is 1/20 of the battery's stated Ah capacity.

So if you want to test your battery to specs, all you need is a 8 amp load and run it for 10 hours.

This should again discharge the battery to around 12.0v, or 50% capacity.

In your case as the battery is known to be down on capacity, you would need to monitor the battery to see how long it takes it to discharge down to 12.0v

It will most likely be a LOT LESS than 10 hours

Some simple math will then give you a pretty good idea as to what your battery's actual capacity is.


If the supplier determines the battery is badly Sulphated, then it is your problem as this is caused by incorrect usage and/or poor maintenance.

Just try desulphating the battery first. You might be in for a pleasant surprise!