BU-905: Testing Lead Acid Batteries

Discover developments in non-invasive rapid-test technologies.

There are no shortages of battery testers, but most lack accuracy. Capacity, the leading health indicator of a battery, is difficult to obtain on the fly. Stating that a battery tester measuring 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 tests can be done with basic methods. Resistance-based instruments can identify a dying or dead battery — so does the user. Vendors often overstate the ability of battery testers knowingly. This is similar to promoting a shampoo that promises to grow lush hair on a man’s bald head.

Without reliable test devices on hand, battery testing becomes guesswork, resulting in good packs being replaced too soon and passing weak ones, only to have them fail on the road 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. Most faults are user-inflicted. 

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 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 through most of their life. Failure due to elevated resistance has become rare and may only develop at the end-of-life. (See BU:901: Fundamentals of Battery Testing.)

Unlike voltage, current and ohmic measurements, no universal instrument exists that can read the capacity of every battery that comes along. There are three common testing concepts: Scalar, vector and EIS with complex modeling (Spectro™).

Scalar is the simplest of the three. It takes a battery reading and compares it with a reference that is often a resistive value. Most single-frequency AC conductance testers measuring CCA are based on the scalar concept.

The vector method applies signals of different currents or it excites the battery with varied frequencies, and then evaluates the results against preset vector points to study the battery under various stress conditions. This adds complexity and the added benefits are marginal.

Spectro™ scans the battery with a frequency spectrum, as if to capture the topography of a landscape, and compares the imprint with a matrix to estimate battery capacity, CCA and SoC. Spectro™ promises the most in-depth battery analysis, but it is also the most complex. (See also BU-904: How to Measure Capacity.). 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 modeling; 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 for battery rapid-testing. The table compares scalar, vector and Spectro™ which combines electrochemical impedance spectroscopy (EIS) with complex modelling.


A matrix is a multi-dimensional look-up table against which 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 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. Most resistance-based testers deliver state-of-health predictions that are not much better than 5 correct in 10, results that can be compared with tossing a coin. Many service technicians are unaware of the low prediction rate as lab verifications are seldom done. 

There is a desire for higher accuracies, but a battery can only be diagnosed if measurable symptoms are present. While packs pulled from the field give the most reliable results, outliers often lack formatting or had been in prolonged storage. To also test these batteries with certainty, matrices can be developed that include the anomalies.

State-of-charge also plays an important role, and the tester must distinguish between low charge and low capacity. Both conditions lower battery performance and are difficult to identify. Most battery testers work down to 70 percent SoC; Spectro™ goes down to 60 percent.

Creating a matrix involves scanning many batteries at different state-of-health levels. The more batteries included in the mix that are the same model but have different capacity losses, the stronger the matrix will become. A well-developed matrix should include naturally-aged battery samples with capacities ranging from 50 to 100 percent. An analogy is a bridge with many pillars to eliminate weak spots.

The population should also include batteries from hot and cold climates and different uses. For example, an aging starter battery in a Las Vegas taxi will show different symptoms than the battery in grandma’s car in northern Germany used only to take her grandchildren for a ride.

Obtaining faded batteries is difficult. Forced aging by cycling in an environmental chamber is of some help, but age-related stresses are not presented accurately and the learned symptoms can fool the system. This is especially visible with Li-ion batteries. Although the capacity is down, the Nyquist plot does not follow the signature of natural aging as part of daily usage. (See BU-907: Testing Lithium-based Batteries.)

A generic matrix is most practical as it serves a group of batteries. Generic matrices for the Spectro™ system are available for most car batteries; the user simply enters the capacity and CCA ratings. Instead of a numeric readout, the generic matrix provides pass/fail classification based on a capacity threshold. This solution is acceptable for most service personnel as the instrument makes the decision, eliminating uncertainties and customer interference.


A battery must undergo multiple checks, the way a medical doctor examines a patient with several tests to find the diagnosis. A serious illness could escape the doctor’s watchful eyes if only blood pressure or temperature were taken. While medical staff is well trained to evaluate the data points taken, most battery personnel do not have the same knowledge and only want to know if the battery is dead or alive. Nor are battery test devices capable of providing a detailed diagnosis of all battery ills. The battery user must be reminded that a battery tester is not a universal test tool but an estimation device that works for a designated battery population.

Last updated 2016-05-27


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Comments (35)

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 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

On November 23, 2016 at 7:06am
Dave Martin wrote:

I’ve tested a car starting battery (rated at 90Ah) on a 6A load and it only gives 11Ah before the voltage starts to drop off rapidly. The supplier is saying that this test is not valid as it is not a deep cycle battery but surely it should be able to supply more than 15% of its rating?

On February 12, 2017 at 10:12am

1)what is DIN series’ battery ?why it called DIN battery? What is its maximum capacity   of DIN range battery ,what is the principal of design & for which application its more suitable .

2)why its container layout and base design change to normal automotive battery.

3)In DIN series why we get more warranty as compare with normal automotive battery.

4)In DIN series battery grid thickness and active material are less as compared to present running automotive battery model but capacity is more why? please describe it.

5)For DIN battery range pest making recipe expender and its specification are different as compare to normal expender which have used in normal automotive battery .

6)For DIN battery add some additive in electrolyte like as tin sulphate , boric acid ,sodium suphate .A)why need to add additive in electrolyte before use?b)In battery industries use two type of electrolyte one for pest mixing and another for battery filling before charging, both type additive quantity ratio are same or different)or additive quantity depend on electrolyte concentration percentage for example-1.400grm/cc,1.200 grm/cc .

7) In Din series battery no need to add DM water why.

8)In Din battery design PE(0.2GM) overall thickness may be around 1.0 mm. Is its different to normal automotive batter at present pos. enveloping PE separator(1.45,1.65)mm why.

9)whate is difference between DIN battery and maintenance free battery.

On May 14, 2017 at 12:56pm
Anita wrote:


DIN is
Deutsches Institut für Normung e.V. is the German national organization for standardization

3)In DIN series why we get more warranty as compare with normal automotive battery
because more $$$$

On May 14, 2017 at 1:00pm
Anita wrote:

To Dave Martin

you are probably totally right, a lot more than 15%
however the battery must be healthy (not sulphated, out of electrolyte…) and fully charged
before the test

the battery may be old, at end of life, many could be
1 fully charge the battery for 15 to 30 hours
measure specific gravity
wait 4 to 8 hours, and repeat your test

On May 22, 2018 at 8:56am
Randy Grenier wrote:

I am reviewing life cycles of forklift 36V lead-acid batteries.  From baseline data to my first quarterly readings of specific gravity and voltage I found that some of the batteries had an increase in specific gravity and a decrease in voltage.  Why is it that when the specific gravity goes up that the voltage doesn’t go up?