How well versed are you in modern automotive battery technologies? Are you able to recognise the various types of batteries in common use today? More to the point though, are you able to explain to your customers why their relatively new batteries sometimes fail prematurely? If truth were told, many of us sometimes fail on all counts, so in this article, we will take a closer look at modern automotive batteries in terms of both their construction, and the common mistakes that we sometimes make when we test car batteries. Let us start with this question-
Broadly speaking, there are only two types of car batteries, these being flooded and sealed batteries. However, the sealed category includes several sub-categories, and it is here where much confusion and wrong diagnostics sometimes combine to shorten the lives of some types of batteries, so let us look at-
These are the batteries we are all familiar with. As a general rule, this type of battery has a liquid electrolyte, and removable caps on each cell that allow for active servicing and/or testing of each individual cell.
The term “sealed battery” applies to a number of different battery constructions, but for the most part, sealed batteries of all descriptions largely follow the same pattern and operating principles as ordinary flooded batteries. However, the term “sealed” suggests that users have no access to the individual cells because these types of batteries generally do not require maintenance and servicing in the conventional sense. It should be noted though that sealed batteries are not really sealed; all sealed batteries incorporate some kind of venting mechanism to allow for some pressure relief of the gases that form in the battery during normal usage. Let us look at some of the main differences between the various types of sealed batteries-
Valve Regulated Lead Acid Batteries
Also sometimes known as Valve Regulated Sealed Lead Acid batteries, this type of battery includes both Gel and Absorbed Glass Mat batteries, and therefore, the abbreviation VRLA is more descriptive of the pressure venting system than it is of a particular battery type. As a rule of thumb, most pressure-relief valves in modern batteries operate in the 2 to 5 PSIG* range to allow for gas recombination cycles to complete in order to maintain the electrolyte level in the battery.
*The PSIG pressure unit expresses pressures relative to atmospheric pressure. For instance, a perfect vacuum would have a PSIG pressure of -14.7, while ambient atmospheric pressure is always expressed as 0 PSIG, regardless of the actual current atmospheric pressure as measured in other units. Based on the PSIG scale, most battery pressure-relief valves would operate in the 1.15 bar to 1.35 bar range.
Absorbed Glass Mat Batteries
While the electrolyte in this type of battery is still liquid, the liquid is absorbed into a finely woven mat of glass fibres, hence the term, “absorbed glass mat”. In practice, the mats of electrolyte-saturated glass are clamped between the metal plates in each cell, which allows for improved discharge and charging efficiencies.
Typical automotive applications of absorbed glass mat batteries include high performance engine starting, such as in race and competition vehicles, as well as in deep cycle batteries that power vehicle accessories. As a rule, the typical absorption voltage of absorbed glass mat batteries is in the 14.4 to 15.0 volt range, while typical float voltages range between 13.2 and 13.8 volts.
Gel Batteries
The single biggest difference between gel batteries and other types of sealed batteries is that the electrolyte is mixed with silica to give the electrolyte a gel-like consistency. While gel cell batteries are more suitable for use in hot climates than other battery types, or where the discharge/recharge cycle is very deep, this type of battery is extremely sensitive to overcharging. In fact, even marginal overcharging with the wrong type of charger will invariably lead to poor battery performance and premature failure of the battery.
However, gel cell batteries are not in common use as LSI (Lights/Starting/Ignition) batteries in standard vehicle applications. These batteries are most commonly used in applications where deep cycling abilities are important, such as for powering accessories in recreational vehicles.
Note that with absorption voltages that typically range between 14.0 and 14.2 volts, and float voltages that typically range from 13.1 to 13.3 volts, the charging profile of gel cell batteries is markedly different from those of other types of batteries.
NOTE: It is important to note that many people, including parts salespersons, often mistakenly refer to gel cell batteries as maintenance-free, sealed batteries. While it is true that gel cell batteries are maintenance-free sealed batteries, gel cell batteries have charging profiles that differ from those of other types of sealed batteries in meaningful ways, so be ultra-careful in selecting a charger for gel cell batteries one hand, and that you are sure that a salesperson does not give you an absorbed glass mat battery when what you want is a gel cell battery, on the other.
Stop/Start Batteries
Stop/start batteries are specifically designed to be able to start a stop-start vehicle multiple times in rapid succession without suffering adverse effects. While most stop/start batteries are of the absorbed glass mat variety, some manufactures have developed, or enhanced simple flooded batteries to the point where they can compete with some absorbed glass mat batteries in terms of cold cranking amps, reserve capacity, resistance to the effects of multiple current drains, and the ability to cope with rapid charge/discharge cycles.
It should be noted though that some battery manufacturers refer to non-absorbed glass mat stop/start batteries as EFB (Enhanced Flooded) Batteries, while others use the term ECM (Enhanced Cyclic) Batteries. It should also be noted that EFB and ECM batteries are essentially the same thing, and are commonly fitted to entry-level stop/start vehicles in which the overall electrical loads on the battery are substantially lower than on high-end start/stop vehicles when the engine is not running. To put the demands on stop/start batteries in perspective, consider the following-
While a conventional electric system/battery is required to start a vehicle on average about 730 times per year, a stop/start system is required to start a vehicle on average about 17 500 per year, which in city driving conditions, equates to one engine start every one to two km. Moreover, while conventional batteries are subjected to minimal cycling, stop/start batteries are almost continuously cycling, while having to supply adequate current to all electrical consumers in a partially discharged state when the engine is not running.
As a result of the very specific power demands and requirements of stop/start vehicles, EFB and ECM batteries have to be replaced with like-for-like replacements. However, it is worth noting that while absorbed glass mat batteries can often be used in place of EFB or ECM batteries, EFB and ECM batteries cannot be used in applications that specifically require absorbed glass mat batteries, which brings us to-
We all understand that a battery’s state of charge, or open circuit voltage can often be a reasonably good indicator of a battery’s overall state of health, but the problem is that we sometimes draw the wrong conclusions from this value.
For instance, do you always test an open circuit voltage directly on the terminals or battery posts, or do you sometimes get this value from the under-bonnet terminals if the battery is located remotely, such as in the boot or under the rear seat? More to the point though, do you always check open circuit voltages only after the battery had recovered from the effects of charging in the vehicle, or do you check the voltage immediately after switching off the engine? In addition, do you use one tester or testing method to test all batteries, regardless of their construction?
If a battery, regardless of its construction or type is well and truly on the point of dying, none of the above matters much, but the above questions take on real meaning and significance in cases where batteries are marginal, or only somewhat suspect. For instance, if you measure an open circuit voltage of say, 9.6 volts during a load test on a remotely fitted battery, does that value take into account the resistance of the cables leading to the engine compartment, does it take into account the temperature of the battery, and is the value obtained from the battery posts directly?
One last question; are you prepared to condemn the battery simply because its open circuit voltage is 9.6 volts, as opposed to the universally accepted value of 9.7 volts, or do you double check your test result with other testing methods?
While experienced technicians are unlikely to answer either “yes” or “no” to all these questions, research conducted by the Battery Council International (BCI) showed that many technicians draw the wrong conclusions when they test batteries because they are not aware of the fact that )among other differences) different types of batteries have different state-of-charge voltages at different temperatures.
Since limited space precludes a comprehensive discussion of these differences, the next best thing we can do is to present a rundown of the basic test procedures that apply to all batteries, as per the Battery Service Manual (available for download at a nominal fee) published by the Battery Council International, starting with-
Load testing
According to the manual, this test involves applying a load of 50% of the battery’s CCA (Cold Cranking Amp) rating for exactly 15 seconds. However, the battery must be at least 75% charged, which generally equates to a rest voltage of at least 12.4 volts. Note though that there is no single test voltage value that applies to all battery types; the tested/measured voltage must be above a limit that depends on the battery’s core temperature of the battery when the test started.
Of course, we cannot know the relationships between battery core temperatures and load-test result that apply to all battery types and/or ratings, nor do we always have the time to allow batteries to rest for 24 hours before performing load tests. Therefore, and although load tests are useful as screening tests, we cannot, and should not rely solely on load tests to determine or assess the overall condition of car batteries.
Conductance testing
Conductance testing involves “injecting” an AC pulse into the battery, the frequency of this signal typically falling into the 80 to 100 Hertz range. This method creates an AC voltage across the terminals that the tester uses to calculate an impedance value, which value is an indicator of the state-of-charge of the battery.
However, it should be noted that while conductance testing is a valuable diagnostic aid, this method can’t replace performance or capacity tests. Therefore, conductive testers that comply with BCI standards will display a definitive test result if the battery is in good condition, or it will tell you to recharge and retest the battery. Note though that this type of test equipment requires that you load the battery’s vital statistics into the tester before starting the test, and that good connections to the battery posts are made to ensure reliable test results.
As with load tests, conductance testing has severe limitations because it cannot accurately measure or assess battery characteristics like reserve capacity or a battery’s ability to sustain cold cranking amps over a given time period. Therefore, the overall health of a battery should not be judged solely on a conductance test result.
Digital oscilloscope testing
Although oscilloscopes typically do not influence, or load down circuits due to their high input impedance(s), they are not particularly useful in identifying battery issues, per se.
However, since oscilloscopes are particularly good at capturing waveforms, an oscilloscope can be used to identify AC voltages that “piggy-back” on DC currents as a result of for instance, some failure modes in alternators that cause over-, or under charging of batteries. Since AC “ripples” in DC currents can be very difficult to identify with other means of testing, we are sometimes over eager to condemn some batteries, while the real cause of the problem might be a marginally defective rectifier in the alternator.
Diagnostic chargers
Essentially, diagnostic chargers combine several advanced diagnostic tools with a limited charging cycle to identify both potential or incipient, and active defects in all types of batteries. In fact, most high-end diagnostic chargers can even distinguish absorbed glass mat batteries that have flat plates from spiral batteries, which are absorbed glass mat batteries in which the plates are wound into coils with the electrolyte clamped between them, which begs this question-
That is not for this writer to say, but he can say that ideally, no single test method should be used as the basis for condemning any battery out of hand, before testing/checking the overall state of health of both the battery, and the vehicle’s electrical system with all appropriate and available test equipment/methods.
The practical advantage of combining tools such as oscilloscopes and diagnostic chargers that can automatically detect the type of battery being tested with reliable service information from reputable battery manufacturers and other reference data (the Battery Service Manual), is that all the guesswork can be removed from battery testing procedures. The fact is that automotive electrical systems are becoming progressively less tolerant of circuit defects, and while component failures other than battery failures cause a large percentage of faults, we need to be sure that our diagnostic methods are capable of definitively confirming, or eliminating battery failures.
More to the point though, we need to be sure that we view our test results in the context of the type of battery being tested, which is an important point to keep in mind, and especially so from a customer service perspective. While we know that it is very difficult, if not impossible to always keep up with which vehicles come to market with which type of battery, we can’t tell our customers that if we want their return business, which leaves us with this-
By using the correct tools and paying attention to the differences between battery types, we can effectively remove the guesswork from battery testing procedures. In practice, this will allow us to definitively identify battery issues, or not, as the case may be, as the cause of electrical issues on our customer’s vehicles.
