BU-905: Testing Lead Acid Batteries

Discover developments in non-invasive rapid-test technologies.

There are no shortages of battery testers, but a closer look reveals that most lack accuracy. The leading health indicator of a battery is capacity, a value that is difficult to obtain on the fly. Stating that a battery tester measuring the internal resistance will also provide capacity estimation is misleading. Advertising features that are outside the equipment’s capabilities confuses the industry into believing that complex test results are attainable with basic methods. Resistance-based instruments work well in identifying a dying or dead battery — but so does the user. Vendors often overstate the ability of their incumbent battery testers and an analogy is promoting a shampoo that promises to grow lush hair on a man’s baldhead.

Without reliable test devices on hand, battery testing becomes guesswork, resulting in good packs being replaced too soon and passing weak ones, causing some to fail soon after checking. Lack of accurate battery testing also causes unnecessary replacements under the battery warranty program. Examining warranty returns reveals that less than 10 percent of these batteries have a manufacturing fault. (See BU-901: Difficulties with Testing Batteries) Furthermore, a battery may be exchanged repeatedly without knowing the cause of the repeat failure. The problem is often outside the battery and the battery manufacturer is being held ransom.

The challenge arises when assessing a battery as part of routine service before performance degradations are noticeable. Such a test is only effective when including a capacity measurement. Capacity oversees the energy storage, governs the runtime and predicts the end-of-life. Internal resistance, on the other hand, is responsible for the power to crank the engine and deliver high current under load on demand. A snapshot taken with a CCA tester on a starter battery refers to the resistive battery condition only. Better electrolytes and corrosion-resistant electrode materials are keeping the resistance on modern batteries low. Failure due to elevated resistance has become rare.

No universal instrument exists that is capable of measuring the capacity of any battery that may come along, as is possible measuring the voltage. Among current methods, scalar is the most simplistic. Scalar takes a battery reading and compares the result with a stored reference is often a resistive value. Most single-frequency AC conductance testers measuring CCA use the scalar concept.

The vector method applies signals of different currents or excites the battery with several frequencies, and evaluates the results against preset vector points to study the battery under various stress conditions. This adds complexity without gaining major benefits and the vector method is not as commonly used as the scalar in form of single-frequency AC conductance.

Spectro™ combines electrochemical impedance spectroscopy (EIS) with complex modeling. It scans the battery with a frequency spectrum as if to capture the topography of a landscape and compares the imprint with a matrix. (See also BU-902a: How to Measure CCA) With appropriate matrices, Spectro can estimate battery capacity, CCA and SoC, providing the most in-depth battery analysis. In spite higher complexity, scientists bet the future in this developing new technology. Figure 1 summarizes the three battery test methods.

Type Excitation Applications Results
Scalar Single reference point; pulses or single-frequency excitation Automotive, stationary; simple, commonly used Voltage, CCA, internal resistance, no capacity
Vector Multiple frequencies, currents; compares against vector Automotive, stationary; less commonly used As above. More complex with marginal gain
Spectro™ Combines EIS with complex modelling; fuses data to derive at capacity, CCA, SoC Lead- and lithium-based batteries Provides CCA, capacity and SoC with appropriate matrices

Figure 1: Methods of data collection. The table compares scalar, vector and Spectro™ which combines electrochemical impedance spectroscopy (EIS) with complex modelling.


A matrix is a multi-dimensional lookup table against which the readings are compared. Text recognition, fingerprint identification and visual imaging operate on a similar principle. In battery analysis, matrices are primarily used to estimate capacity; however, CCA and state-of-charge will also benefit from using a matrix.

Spectro™ correctly predicts 8 out of 10 batteries on capacity, and 9 out of 10 on CCA. Combining these two classifications provides significant improvement in test accuracies over units measuring only CCA. Many resistance-based testers deliver state-of-health predictions that are not much better than 5 correct in 10, a result that can be compared with tossing a coin. Many service personnel are unaware of the low prediction rate as lab verifications are seldom done. 

There is a desire for higher accuracies but the industry must understand that a battery can only be diagnosed if measurable indicators are present. Best results are achieved when testing a battery that is pulled from the field. New batteries that have not been fully formatted or have been in storage provide less accurate results because the symptoms may be skewed. In addition, a battery with low capacity and a battery with a partial charge have similar visible pointers and the test method must distinguish between these two deficiencies.

Separating capacity, CCA and SoC as separate battery identities is a challenge and cannot be fully satisfied. Most battery testers work within a SoC range from 60–100 percent. If too low, the device prompts to charge and retest.

Creating a matrix involves scanning many batteries at different state-of-health levels. The more batteries that can be included in the mix of same model but different capacity, the stronger the matrix will be. A well-developed matrix should include battery samples with capacities ranging from 50 to 100 percent. This provides a solid span that resembles a bridge with many pillars. The population should include batteries from hot and cold climates with diverse user patterns. For example, a starter battery in a Las Vegas taxi experiences different stress levels than in grandma’s car cruising in the countryside of northern Germany.

It can be difficult to obtain faded batteries, especially with newer models. Forced aging by cycling in an environmental chamber is of some help but age-related stresses are not being presented accurately and the formed symptoms can fool the system.

Generic matrices serving a group of similar batteries are most practical and there is a move towards the generic solution. One tester can service most car batteries by simply selecting the capacity and CCA rating but the result is in a pass/fail classification based on a capacity threshold. This is acceptable for most service personnel as the instrument makes the final decision, eliminating uncertainties and customer interference.


A battery check must undergo multiple tests and an analogy is a medical doctor who examines a patient with several instruments to find the diagnosis. A serious illness could escape the doctor’s watchful eyes if only blood pressure or temperature was taken. While medical staff is well trained to evaluate data points taken, most battery personnel do not have the knowledge to read a Nyquist plot and other data on a battery scan. Nor are test devices available that give reliable diagnosis of all battery ills. A user of a battery test device must be reminded that a battery test is not a measurement per se but estimation by looking at several symptoms. Some basic education in testing batteries is a prerequisite.

Last updated 2015-05-21


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On July 7, 2011 at 2:39am
Paul wrote:

Just what I was looking for. Now tell where I can get the algorithm to put into my own Solar controller design..

On November 24, 2011 at 2:53am
Virendra Anand wrote:

How do I reduce water loss in my lead acid battery

On December 17, 2011 at 9:36am
s.srinivas wrote:

please mention the way of testing LAcells for internal resistance,capacity of bank with out disconnection from loads .

On March 23, 2012 at 12:03am
Smitha wrote:

We would like to purchase the Spectro CA-12 battery tester.
Please clarify the below questions also
1. What are the parameters to be tested with this battery tester?
2. What is the maximum current and volage ?
3. What is the maximum allowable dicharge current of battery?
4. What is price(To India)
5. Whether we can check all types of batteries like, NimH, LEad Acid, Lithium ion etc.
6. Whether we can check the battery capacity in AH.

On April 27, 2012 at 10:04pm
norozi wrote:

hello dears
what kind of load we can apply for 12v lead acid battery during this test

On May 1, 2012 at 6:46am
Jeff Kral, Jeff Skis & Machines Inc. wrote:

I am looking to purchase one of these Spectro CA-12 units. Please send me the info on how to do so.

On May 20, 2012 at 7:53am
B.K.Anand wrote:

Hello, I have a 800 VA home ups, it is working fine for last one year, but from past 15 days both inverter and battery are heatng and very hot, please give smart solution

On July 9, 2012 at 8:38pm
Saravanan wrote:

What is the testing process of Battery grade acid and DM Water?

On July 9, 2012 at 8:40pm
Saravanan wrote:

Using Agno3 how and what is the testing process of brattery grade acid and DM water?

On July 12, 2012 at 6:52pm
Le Thanh Hung wrote:

I am looking for deep cycle battery tester

On July 12, 2012 at 6:56pm
Le Thanh Hung wrote:

I am looking for deep cycle battery tester. Please give me more information about this tools.

On October 17, 2012 at 1:39pm
pat harris wrote:

how can I tell if battyert good??——charged battery and meter said 12 volts….then i tested the acid with a flooting ball mesurmernt———On test it show 2 cells deat OR no balls floating,,,,is that possible???l

On December 30, 2012 at 11:31pm
ALIREZA wrote:


On January 21, 2013 at 10:47am
Anthony Maskens wrote:

I have two banks 12volt 135amp hr starter batterise coulpled to give 24vlts. Plese can you advise me on device to measure the capacity to measure the required output for starting requirements. the batteries are situated on a boat so a hand held would necessitate, Many thanks in anticipation. Ps also a purchase price would be appreciated.
Anthony Maskens

On March 17, 2013 at 5:38am
Brand van Deventer wrote:

What test can be done on a lead acid starter and/or deep cycle battery using multi tester when time is no problem. Example:- A 135 Ah deep cycle battery, charged to 14.3V (maintenance) is connected to a 120 watt globe (120W/12V=10 amp OR should it be 120W/14.3=8.4amp?) and Voltage is measured every 30min.

What should the Voltage (or any other reading be) for a battery in good health at every 30 min. interval?

On March 17, 2013 at 6:17am
Alex Guimarães wrote:

Dear alll

How can i buy the spectro CA12 in Brazil, do You have representative in our country.
Please send An. Answer with contact.

Best Regards,

Alex Guimaraes

On April 24, 2013 at 2:48am
Muthuramalingam.E wrote:

Please Battery Testing Program in Training

On June 20, 2013 at 10:32pm
Jason Blair wrote:

to B.K.Anand please disconnect your UPS NOW!!! The battery is in a thermal runaway condition and could cause a fire

Jason Blair
First Logistex Inc

On August 10, 2013 at 2:30pm
dogphlap wrote:

Looking at my previous comment I see it is not as clear as it should have been.
This formula is what I meant to imply.
E=V -.004Vt
where V=cell (or battery) voltage prior to temperature change.
where t= temperature change in degrees centigrade.
where E=the new cell voltage post the change in temperature.

I just posted this correction in case someone claimed my last post meant a lead acid battery would only have a terminal voltage of 40mV at 10 degrees centigrade (literally that is what I said but not what I meant).

I’d still like a creditable source and or a better formula if anyone has one.

Best regards dogphlap

On August 10, 2013 at 2:39pm
dogphlap wrote:

Sorry, wrong again. Should be:
E=V -.004Ct
where V=cell (or battery) voltage prior to temperature change.
where t= temperature change in degrees centigrade.
where E=the new cell voltage post the change in temperature.
where C=the number of cells in the lead acid battery.

Best regards dogphlap.

On August 10, 2013 at 2:48pm
dogphlap wrote:

I wish I could edit these posts.
E=the new battery voltage (not cell voltage).

Best regards dogphlap.

On August 21, 2013 at 4:05am
VIDEjO wrote:


On January 14, 2014 at 9:31am
shafiqur rahman wrote:

i think i can learn much of this page!  Thanks alot!

On July 5, 2014 at 11:45pm
shiva kumar Hyd wrote:

Its really informative

On July 16, 2014 at 8:27am
MM Ali wrote:

Anyone using the CADEX equipment to test, maintain and service 2V high capacity [500 - 3000 AH] battery?

Any information will be helpful.

Best Regards

On July 16, 2014 at 8:29am
MM Ali wrote:

Is anyone using CADEX for testing, maintaining and servicing [Wet & Dry] batteries of higher capacity of 500 to 3000 AH.

Any help will be highly appreciated.

Best Regards

MM Ali

On August 2, 2014 at 3:08am
Itazaz wrote:

I have a 180 AH battery with 1000 VA UPS at my home. from last 30 days both are heating up and battery takes a lot of time to get charged with electrolyte evaporation as well. plz suggest a smart solution that how can I revive battery life.

On September 13, 2014 at 1:07am
Carrick wrote:

Hi Everyone
How I can test single plates in battery (plates before assembly). And what parameters effect in this result? Example: weight of active material, porosity,... Many thanks!

On November 13, 2014 at 5:27am
suresh patil wrote:

If lead acid battery has to be tested at 20 hr. rate, 10 hr. rate, 5 hr. rate and 3 hr. rate, is there a recommended sequence of test to get accurate results? If high current discharge test is done first prior to low current discharge, will the result give correct AH capacity?

On December 30, 2014 at 9:39pm
Andrew Hale wrote:

Questions ,Questions….but no answers!

On January 3, 2015 at 2:55pm

we are looking for one electomic circiut for lead acid Battery simulation more than 800 Ah, in order to test battery chargers .
can you please inform ?
thank you