Interesting correlation between CCA and battery residual capacity

[cyclopathic]

https://batteryuniversity.com/artic...tery-capacity-and-resistance-as-part-of-aging

Looks like you lose ~50% capacity while you still have over 75% CCA. Is it why many battery testers would discard battery if CCA goes below 80%?

 

[Donald]

https://batteryuniversity.com/artic...tery-capacity-and-resistance-as-part-of-aging

Looks like you lose ~50% capacity while you still have over 75% CCA. Is it why many battery testers would discard battery if CCA goes below 80%?

Assuming everything on the webpage is accurate.

 

[eljefino]

My off grid camp has four dual purpose marine batteries in series for the solar system. The fridge runs all night and morning coffee puts a load on that brings each battery down to 8-9 volts. Clearly it's not great to run all the way down but its also a great way to see capacity is still what it was in fall of 2022 when I got the batteries.

I have also seen low capacity batteries-- the group 65 in my town car could start at -10f, and if it couldn't a half hour on a one amp trickle charger would fix it. Continued charging did nothing as the battery simulated being full.

Had a 2nd gen Prius that complained about not being in Park after listening to the radio for five minutes after shutoff. That battery didn't even have to crank an engine so it was very far gone.

In short, OP links to a very good point, one that doesn't get tested much because it's "bad" to discharge car batteries below what's needed to start.

 

[Cmobile]

Good article, thanks for sharing.

 

[Number_35]

@cyclopathic, good article, thanks for sharing it.

The A-h capacity vs. CCA capacity jibes with my experience. I've had a couple of marginal batteries that passed a CCA load test (100 A for 10 s) fine, but failed an A-h test badly.

I have a Schumacher CCA tester - basically a big resistive element with a voltmeter.

I've also rigged up a system with the battery-under-test feeding a 12 VDC to 120 VAC inverter, which then powers an analog electric clock that runs on 120 VAC. There's also an incandescent lightbulb to increase the load. (I deserve no credit for this rig - I saw it online.)

You start with the battery fully charged, and then apply the load, measuring current with an ammeter.

The inverter cuts out when the battery drops to c. 10.5 V, and the clock stops. (That's why it needs to be an analog clock; a digital clock would simply cut out without recording how long it had run.)

If the load was 8 A and it took 2 hours for the clock to stop, the battery's A-h capacity is only 16 A-h.

Given that a typical battery would be rated more like 50 A-h, 16A-h puts it at < 33% of rated capacity, and ready to fail.

So why doesn't this show up in a CCA test?

100 A x 10 s = 1000 A-s/3600 s/hour = < 0.3 A-h. It's not a good test of the battery's capacity.

 

[JHZR2]

Capacity (mass of active material) and rate capability (impedance) are only correlated but so much.

You can have tiny batteries with huge current capabilities, and giant high energy batteries with next to none.

Starting batteries are balanced with a bias towards rate. Of course a reduced cca will mean higher voltage drop (lower voltage) due to increased impedance, but there can still be a ton of active material that will give capacity under low current discharge. Batteries often fail the other way. Sometimes there is a lot of shed material, so the voltage will show good, but it will collapse when started because there is no capacity and the impedance is high.

 

[Cmobile]

I remember when I managed Fire Alarm Control systems. There were two small 9AH SLA batteries in each panel, maybe 20-25 panels throughout the hospital. Every 3 years all batteries got changed out, but they were tested every year. Maybe a handful didn't pass after year 2.

The organization purchased an expensive tester, "Cell Checker" brand, which i think looks at V, SoC, AH, and provides a percentage od health. Our policy was they had to test over 90%.

Kinda wish I could afford to have a unit like this. They retail for about $700.

Here is the unit,

 

[cyclopathic]

@cyclopathic, good article, thanks for sharing it.

The A-h capacity vs. CCA capacity jibes with my experience. I've had a couple of marginal batteries that passed a CCA load test (100 A for 10 s) fine, but failed an A-h test badly.

I have a Schumacher CCA tester - basically a big resistive element with a voltmeter.

I've also rigged up a system with the battery-under-test feeding a 12 VDC to 120 VAC inverter, which then powers an analog electric clock that runs on 120 VAC. There's also an incandescent lightbulb to increase the load. (I deserve no credit for this rig - I saw it online.)

You start with the battery fully charged, and then apply the load, measuring current with an ammeter.

The inverter cuts out when the battery drops to c. 10.5 V, and the clock stops. (That's why it needs to be an analog clock; a digital clock would simply cut out without recording how long it had run.)

If the load was 8 A and it took 2 hours for the clock to stop, the battery's A-h capacity is only 16 A-h.

Given that a typical battery would be rated more like 50 A-h, 16A-h puts it at < 33% of rated capacity, and ready to fail.

So why doesn't this show up in a CCA test?

100 A x 10 s = 1000 A-s/3600 s/hour = < 0.3 A-h. It's not a good test of the battery's capacity.

I'll try to find an article but basically the batteries are rated at 10h discharge rate, and at 1-2hr lead-acids (flooded, AGM,Gel, etc) only register 40-50% of rated capacity. LifePO4s can manage 80-90% of rated capacity under similar loads