What causes car batteries to fail early?
Driving habits rather than battery defect may
be the cause
German manufacturer of luxury cars reveals that of 400 SLI batteries returned
under warranty, 200 are working well and have no problem. Low charge and acid
stratification are the most common causes of the apparent failure. The car manufacturer
says that the problem is more common on large luxury cars with power-hungry auxiliary
options than on the more basic models.
In Japan, battery failure is the
largest complaint among new car owners. The average car is only driven 13 km (8
miles) per day and mostly in a congested city. As a result, the batteries will
never get fully charged and sulfation occurs. The batteries in Japanese cars are
small and only provide enough power to crank the engine and perform some rudimentary
functions. North America may be shielded from these battery problems, in part
because of long distance driving.
Good battery performance is important
because problems during the warranty period tarnish customer satisfaction. Any
service requirement during that time is recorded and the number is published in
trade magazines. This data is of great interest among prospective car buyers throughout
Battery malfunction is seldom caused by a factory defect; driving
habits are the most common culprits. Too much electrical power may be drawn in
the distance driven. As a result, the battery does not receive the periodic fully
saturated charge, a requirement that is so important for the longevity of a lead
acid battery. According to a leading European manufacturer of car batteries, factory
defects amounts to less than 7 percent.
Getting a fast and dependable
assessment of a failing battery is difficult. Most battery testers in use only
take cold cranking amps (CCA) and voltage readings. Capacity, the most important
measurement of a battery, is unavailable. While taking the CCA reading alone is
measuring the capacity is very complex and instruments
offering this feature are expensive. For this reason, most capacity measurement
instruments are still based on applying a full discharge and recharge. This procedure
is typically used in a laboratory environment. Time would not permit this for
the service sector.
The Spectro CA-12 by Cadex Electronics is the first
in a series of high-end battery testers that is capable of measuring capacity,
CCA and state-of-charge (SoC) in a single, non-invasive test. The technology is
based on multi-model electrochemical impedance spectroscopy (EIS). The system
injects 24 excitation frequencies ranging from 20 to 2000 Hertz. The sinusoidal
signals are regulated at 10mV/cell to remain within the thermal battery voltage
of lead acid. This achieves stable readings for small and large batteries.
the 30-second test, over 40 million transactions are completed. A patented algorithm
analyses the data and the final results are displayed in capacity, CCA and state-of-charge.
The Spectro CA-12 for automotive batteries is shown in Figure 1.
1: Spectro CA-12 automotive battery tester. |
This instrument is the
first in a series of battery testers that displays capacity, CCA, and state-of-charge.
A patent using multi-model electrochemical impedance spectroscopy has been granted
to Cadex Electronics.
Advanced battery testers
are set to work within a preconfigured test range. Unlike a photocopier that duplicates
any document that is placed on the glass, a high-end battery rapid-tester needs
to know battery type, rated capacity, CCA and voltage. In addition, a matrix is
required against which the readings are compared. These matrices cover the common
flooded SLI family, the deep cycle batteries, the Absorbent Glass Mat (AGM), the
spirally wound design, and the gelled type used for wheelchairs and people movers.
Matrices can also be developed to test lithium and nickel-based batteries. The
Spectro CA-12 is capable of storing 5 menu-selectable matrix sets to service the
most common battery groups.
When available early next year, the Spectro
CA-12 will include the most common matrices. New matrices can be added by scanning
batteries of the same model and various performance levels with the CA-12 running
on a special program. Before scanning, the batteries must be prepared with a defined
discharge/ charge program. With the help of the PC-Companion software, the collected
data is sent to Cadex where the engineers assemble the code and return a working
matrix to the user for download into the tester.
Bar coding car batteries
A German luxury car manufacturer has introduced a system that
embeds vital battery information in a bar code label. The
label also contains the battery serial number and manufacturing
date. When checking batteries with a tester that supports
a bar code scanner, the technician only needs to scan the
bar code label and the instrument is automatically configured
to the correct battery. Battery testing is thus simplified
to scanning the label, attaching the leads to the battery
and reading the test results.
Figure 2 illustrates such a test in process.
||Figure 2: Bar coding
car batteries to simplify testing.
The technician reads the bar code label and the CA-12
automatically configures to the correct battery type.
The test results and battery serial number can be downloaded
into a PC running Cadex Companion software.
Bar coding car batteries simplifies battery testing, eliminates
configuration errors and allows less trained technicians to
perform the service. The accuracy is also improved because
the system selects the most suitable matrix. Batteries, which
have no bar code can be upgraded by adding a permanent label.
The battery data and serial number are entered into the PC,
the Companion software translates the information into the
bar code format and a label printer generates the adhesive
label. Once labeled, subsequent testing on this battery will
To eliminate unauthorized warranty claims, a process can be
introduced in which both the battery serial number and the
car chassis number are required. A battery replacement is
only offered if the information is correct. Another system
to keep honesty is generating warranty numbers that accompany
the battery and paperwork of a faulty battery back to the
manufacturer for replacement.
Acid stratification, a problem with luxury cars
A common cause of battery failure is acid stratification.
The electrolyte on a stratified battery concentrates on the
bottom, causing the upper half of the cell to be acid poor.
This effect is similar to a cup of coffee in which the sugar
collects on the bottom when the waitress forgets to bring
the stirring spoon. Batteries tend to stratify if kept at
low charge (below 80%) and never have the opportunity to receive
a full charge. Short distance driving while running windshield
wiper and electric heaters contributes to this. Acid stratification
reduces the overall performance of the battery.
Figure 3 illustrates a normal battery in which the acid is
equally distributed form top to bottom. This battery provides
good performance because the correct acid concentration surrounds
the plates. Figure 4 shows a stratified battery in which the
acid concentration is light on top and heavy on the bottom.
A light acid limits plate activation, promotes corrosion and
reduces performance. High acid concentration on the bottom,
on the other hand, artificially raises the open circuit voltage.
The battery appears fully charged but provides a low CCA.
High acid concentration also promotes sulfation and decreases
the already low conductivity further. If unchecked, such a
condition will eventually lead to a user-induced battery failure.
||Figure 3: Normal battery
The acid is equally distributed from the top to the bottom
in the cell and provides maximum CCA and capacity.
||Figure 4: Stratified
The acid concentration is light on top and heavy on the
bottom. High acid concentration artificially raises the
open circuit voltage. The battery appears fully charged
but has a low CCA. Excessive acid concentration induces
sulfation on the lower half of the plates.
Allowing the battery to rest for a few days, applying a shaking
motion or tipping the unit over tends to correct the problem.
A topping charge by which the 12-volt battery is brought up
to 16 volts for one to two hours also reverses the acid stratification.
The topping charge also reduces sulfation caused by high acid
concentration. Careful attention is needed to keep the battery
from heating up and losing excessive electrolyte through hydrogen
gassing. Always charge the battery in a well-ventilated room.
Accumulation of hydrogen gas can lead to an explosion. Unlike
many other gases, hydrogen is odorless and can only be detected
with measuring devices.
of battery testing
Acid stratification is difficult to measure, even with the
EIS technology. Non-invasive testers simply take a snapshot,
average the measurements and spit out the results. Stratified
batteries tend to show higher state-of-charge readings because
of elevated voltage. On preliminary tests, the Spectro CA-12
also shows slightly higher CCA and capacity readings than
normal. After letting the battery rest, the capacity tends
to normalize. This may be due to diffusion effects in the
stratified battery as a result of resting. Little information
is available on how long a stratified battery needs to rest
to improve the condition. It is known, however, that higher
temperatures will hasten the diffusion process.
Ideally, a battery tester should indicate the level of acid
stratification; sulfation, surface charge and other such condition
and display how to correct the problem. This feature is not
yet possible. Much research is being done in offering more
complete battery evaluation without the need to apply a full
discharge. This knowledge can then be applied to other battery
systems, such as traction, military, marine, aviation and
During the last 20 years, battery testing lagged behind other
technologies. One of the reasons: The battery is a very difficult
animal to test, short of applying a full charge, discharge and
recharge. The battery behaves similar to us humans. We still
don't know why we perform better on certain days than others.
Even by using highly accurate charge and discharge equipment,
batteries produce disturbingly high capacity fluctuations. To
demonstrate this phenomenon, Cadex tested over 100 car batteries
with diverse performance levels (Figure 5). We first prepared
the batteries by giving them a full charge and a 24-hour rest
period. We then measured the capacity by applying a 25A discharge
to 10.50V or 1.75V/cell (black diamonds). This procedure was
repeated for a second time and the resulting capacities were
plotted (purple squared). There was a whooping +/-15% variation
in capacity readings across the full population. Some batteries
had higher readings the second time; others came in lower. Portable
nickel and lithium-ion batteries appear to be more consistent
in capacity readings than lead acid. More research will be needed
to find the apparent instabilities of lead acid batteries.
5: Capacity fluctuations
Capacities of 113 car batteries measured with a conventional
discharge method show a fluctuation of +/-15%.
For the longest time, load testers have been the standard test
method for car batteries. The year 1992 brought us AC conductance,
a method that simplified battery testing. Now we are experimenting
with multi-model electrochemical impedance spectroscopy (EIS)
in a portable version at an affordable price.
EIS is very complex and until recently required dedicated computers
and expensive laboratory equipment, not to mention chemists
and engineers to interpret the readings. The hardware of an
EIS system is commonly mounted on racks and the installation
runs into tens of thousands of dollars. High-speed digital signal
processors and advanced data analysis made it possible to package
this technology into a hand-held device.
One of the major drawbacks of older technologies is the inability
to measure battery capacity. CCA alone tends to be misleading
because state-of-charge and other battery conditions affect
the readings. Capacity is a pivotal measurement that assesses
the battery condition most accurately.
No battery tester solves all problems. Entry-level testers have
the advantage of being low cost, simple to use and capable of
servicing a broad range of batteries. However, these units only
provide a rough indication of the battery condition. Most units
have poor failure detection capabilities and simply indicate
'good battery', 'recharge battery' or 'fail'. A lab test at
Cadex demonstrates that a battery tester based on EIS is four
times more accurate in detecting weak batteries than AC conductance.
In addition, the EIS technology can be configured to show capacity,
CCA and state-of-charge readings in numbers and in percentage
of the nominal value. Figure 6 shows such display formats.
||Figure 6: Displays
CCA, RC and SoC of the Spectro CA-12.
The results are displayed in numbers and in percentage
of the nominal value.
test results are important to engineers in a battery research
laboratory, an accurate pass/fail detection method is often
sufficient for the service sector. The technician simply needs
to know if a failing battery requires recharging or replacing.
Conventional testers often misjudge the battery on account of
low state-of-charge. Many batteries are replaced when they should
have been recharged, while others are given a clean bill of
health when it should have been replaced. With an quick and
accurate battery test system, returned batteries can be tested,
charged and kept ready for an eventual replacement. Such a program
would speed up service, enhance customer satisfaction and save
About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc., in Vancouver BC. He has studied the behavior of rechargeable
batteries in practical, everyday applications for two decades.
Award winning author of many articles and books on batteries,
Mr. Buchmann has delivered technical papers around the world.
Isidor Buchmann is the founder and CEO of Cadex Electronics
Inc., in Vancouver Canada. Founded in 1980, Cadex specializes
in the design and manufacturing of advanced battery charging
and testing instruments. For product information please visit