What causes car batteries to fail early?
Driving habits rather than battery defect may be the cause

Isidor Buchmann
Cadex Electronics Inc.
isidor.buchmann@cadex.com
www.buchmann.ca
June 2004

A 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 the world.

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 relatively simple,
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.

During 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.

Figure 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 be simplified.

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 battery 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.

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 stationary batteries

Figure 5: Capacity fluctuations Capacities of 113 car batteries measured with a conventional discharge method show a fluctuation of +/-15%.

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.