BU-806: Tracking Battery Capacity and Resistance as part of Aging

Learn about CCA characteristics and capacity fade and how they diverge with age.

All batteries age and the effects manifest themselves in diminished capacity, increased internal resistance and elevated self-discharge. A new battery (Figure 1) delivers (or should deliver) 100 percent capacity; an aged unit (Figure 2) may hold only 20 percent. In our example, the capacity loss is illustrated by placing rocks in the container.

New battery has high capacity Figure 1: New battery has 100% capacity. Capacity is represented by a liquid with no obstruction. The battery delivers full runtime.
Courtesy of Cadex
Aged battery has low capacity Figure 2: Faded battery. Capacity loss is illustrated as “rock-content.” The battery behaves normally but it has a short runtime, even if fully charged.
Courtesy of Cadex

Automotive technicians are most familiar with CCA (cold cranking amps) in relation to turn the engine. CCA relates to the internal battery resistance and the ability to deliver high load current. Figure 3 illustrates a starter battery with high CCA and an open tap symbolizing delivering full power; Figure 4 has elevated internal resistance that limits the current delivery to a trickle.

Battery with high CCA

Figure 3: Low internal resistance enables high current. Cranking current on a starter battery is 300A; a golf car draws 56A
Courtesy of Cadex

Battery with low CCA Figure 4: Battery with low CCA. Rising internal resistance inhibits power delivery. This is less common as capacity fade occurs first.
Courtesy of Cadex

Rechargeable batteries have improved and maintain low internal resistance during most of the service life; an increase in internal resistance may only occur towards the very end. Starter batteries keep a high CCA and provide healthy cranking to the end, but the capacity gradually drops without sign. An analogy is a galloping horse that keeps its spirited performance until its eventual collapse from exhaustion. Figure 5 demonstrates the relationship of capacity and CCA of 20 aging starter batteries, sorted according to capacity. (See also BU-905a: Testing Starter Batteries in Vehicles.)

Capacity and CCA readings of 20 aging batteries
Figure 5: Capacity and CCA readings of 20 aging batteries. Batteries 1–9 have good CCA and high capacity; the CCA of batteries 10–20 still enables good cranking, but the batteries have large capacity loss. CCA tends to remain high while the capacity drops with aging. Test method: CCA was estimated with the Spectro CA-12 and the capacity was measured with an Agilent load bank by applying full discharges according to BCI standards.
Courtesy of Cadex

Batteries 1–9 perform well on capacity and CCA, but batteries 10–20 show notable capacity loss while maintaining acceptable CCA performance. Capacity depletion eventually disables the cranking. This is mostly evident during cold spells, which further reduce the capacity.

Car manufacturers often use 65 percent as the pass/fail threshold for warranty replacement while service garages take 40 percent as an end-of-life indication. (See BU-904: How to Measure Capacity.) Forty percent should give another 6–12 months of service, but below this is cause for concern and the battery should be replaced even though the cranking is still good. Thrifty drivers (including the author), prefer to wait but invariably get caught with a dead battery at the worst possible moment.

To study the correlation between capacity and internal resistance, Cadex tested 175 aging starter batteries by measuring the CCA and capacity according to SAE J537. In this lengthy test, Cadex found that the correlation between capacity and CCA is only 0.55 (1 would be a perfect match). This led to the development of capacity estimation technology, as relying on the internal resistance, or CCA on a starter battery is unreliable. Figure 6 demonstrates the aging trend of starter batteries as a function of capacity and CCA.(See BU-1101: Glossary under SAE J537)

Reserve Capacity
Figure 6: Relationship between CCA and capacity of 175 starter batteries. Batteries in the green PASS field are functional; the red FAIL field denotes breakdown. Most batteries exit life through the 40% capacity line at the left field; few slip through the 50% CCA line. Test method: Capacity and CCA were tested accoding to SAE J537.
Courtesy of Cadex

The horizontal X-axis represents capacity; the vertical Y-axis shows CCA; the stars are the 175 batteries tested. The arrow shows the typical aging trend of batteries passing through the “Capacity Line” on the left PASS field. Very few batteries slip through the “CCA Line.”

This demonstrates that starter batteries fail mainly due to capacity fade rather than low CCA or elevated internal resistance. This characteristic is visible with most lead- and lithium-based batteries. A capacity measurement is more meaningful than measuring the internal resistance, but estimating capacity on the fly involves higher complexities than simply taking an ohmic reading.

Last updated 2018-01-23

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Comments (9)

On March 21, 2012 at 3:30pm
Sanjay wrote:

Give full knowledge vrla battery

On March 29, 2013 at 1:44am
Pete wrote:

Hi, I have a car battery that turns my diesel engine fast - (high CCA (cold cranking amps), but only last for about 5 seconds when cranking, then stops cranking and the battery is drained. Its an old battery - aprox 10 years, its been desulfated because at one time wouldn’t even turn the engine after a full charge. Is their anyway of adding chemicals to improve the capacity of the battery? thanks Pete

On January 6, 2014 at 1:37pm
Brett wrote:

I worked at Sears and J.C. Penney auto centers for over 10 yrs combined. I never saw a battery last 10 yrs. 5 years is doing real good. If you got 10 God loves you, but it’s time to get up off the wallet and buy a new one. You don’t wanna get caught out in some God awful place with a dead battery trying to save a couple of bucks.  Take that advice for what it may be worth.

On March 7, 2014 at 12:25am
Edward Thirlwall wrote:

I’m assuming we are only referring to the fuel-driven types of batteries here, but what would the difference be to an electrically charged battery? For electric cars, I’m sure the battery in itself works similarly in terms of storage and capacity and output as well? In addition, it would help to have a form of comparison so that consumers can really look at cost-benefit analysis of the different types.

On September 10, 2014 at 7:34am
AMjad Akx wrote:

Can u tell me how to check a battery percentage with a multimeter.

On March 20, 2015 at 10:42pm
Andrew wrote:

I get 10 years out of all my car batteries, although one did get sluggish after 7 years.
I always keep the electrolyte topped up and apply a float charge once a week for 12 hours.
Most of our driving is city/small runs, so I`m always careful to keep the batteries fully charged via the float charger. I use the Battery Fighter charger.

On March 25, 2015 at 4:37pm
Ann wrote:

Would there be permanent damage to any type of mobility scooter battery if it had been stored from new for 2 years and never used.

On July 3, 2015 at 8:59pm
m8ty.com wrote:


Yes, if its a lead acid battery there should be permanent damage if you stored it for two years and never charged it.  As you can see, all lead acid battery have a natural discharge rate between 1% to 20% monthly, so at 20% monthly your battery would be 100% discharged in just 5 months and that is using the worst case scenario discharge rate, at the ultra conservative 1% discharge rate, your battery would be 24% discharged within two years, but I highly doubt it that your battery was discharging at just 1%, you can take 5% to be a more conservative realistic discharge value and if your battery was discharging at a rate of 5% per month, that is 60% discharge in one year so at this rate it would take 20 months to completely discharge your battery - from 12 volts all the day down to 0 volts and that’s not taking under consideration that permanent damage starts if you let a lead acid battery discharge below 10.0 volts, thats why most power inverters have a cut off at 10.5 volts in order to prevent damage to the battery.

So, it is safe to assume your lead acid battery that hasn’t been used or charged a single time for 2 years straight up is completely and irreparably sulfated. 

For future reference I would suggest getting a trickle (maintenance) charger and keep it connected to your battery(ies) you wish to keep in long term storage in order to keep them fresh and functional when you need them.

On August 22, 2016 at 11:40pm
Mark Adams wrote:

I am re-writing some planned maintenance work procedures for my Company’s 3 fleets of ships. Each ship has upwards of 80 different batteries on board. Some are deep-cycle. Some, like radio batteries, big control system back-up batteries, have low current draw, are on trickle float-charge continuously and are are critical. The rest and most are Li-ion, NiCad etc, depending on what the ship-builder supplies. We have a 2.5-3 year renewal program for all these minor ones. We have a fair few of these big, expensive to renew batteries and we need a simple method of routine testing and, most important, logging the results to give us an indication of when they are below the 80% capacity recommended in your excellent pages.
I am proposing the simple, Fluke multimeter method for the deep-cycle, starter-motor batteries as follows:

“1/ If you are able, measure the density of each cell using a hydrometer.
2/ Switch-off charger. Then measure voltage acrosss the terminals. Record the voltage.
3/  Wait for 30 minutes. Take and record voltage again.
4/ Switch-on the charger
5/ Connect Multimeter across ONE 12v battery.
6/ Press MIN/MAX button on Multimeter to get max/min voltages
7/ Start engine.
8/ When finished checks on engine, stop engine.
9/ Disconnect the Multimeter
10/ Record the min/max voltages on the Sheet
11/ Carry-out the test on other engine starting batteries.”

The issue I have is how to check/test the radio batteries etc as these are, (usually), large, single-cell, sealed units. 12 of these are linked together to form a ‘battery’ of 12v. We cannot switch-off the charger for 10 hours to see what happens for safety reasons so what maintenance instructions do you suggest I can use? The ships don’t carry a load-bank as this test is only required once a year. We are further disallowed to carry-out a deep discharge.