BU-806a: How Heat and Loading affect Battery Life

Learn about the temperature and how start-stop shortens the life of a starter battery

Heat is a killer of all batteries, but high temperatures cannot always be avoided. This is the case with a battery inside a laptop, a starter battery under the hood of a car and stationary batteries in a tin shelter under the hot sun. As a guideline, each 8°C (15°F) rise in temperature cuts the life of a sealed lead acid battery in half. This means that a VRLA battery for stationary applications specified to last for 10 years at 25°C (77°F) would only live 5 years if continuously exposed to 33°C (92°F) and 30 months if kept at a constant desert temperature of 41°C (106°F). Once the battery is damaged by heat, the capacity cannot be restored.

According to the 2010 BCI Failure Mode Study, starter batteries have become more heat-resistant. In the 2000 study, a rise in temperature of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has been widened to 12°C (22°F). Other statistics reveal that in 1962, a starter battery lasted 34 months; technical improvements increased the life expectancy in 2000 to 41 months. In 2010, BCI reported an average age of 55 months for starter batteries, with the cooler North attaining 59 months and the warmer South 47 months. Colloquial evidence in 2015 revealed that a battery kept in the trunk of a car lasted one year longer than if positioned in the engine compartment.

The life of a battery also depends on the activity, and the service life is shortened if the battery is stressed with frequent discharge. Cranking the engine a few times a day poses little stress on a starter battery, but this changes in the start-stop operation of a micro-hybrid. The micro-hybrid turns the internal combustion engine (ICE) off at red traffic lights and restarts it when the traffic flows again, resulting in about 2,000 micro-cycles per year. Data obtained from car manufacturers shows a capacity drop to about 60 percent after 2 years of use. To increase cycle life, automakers use specialty AGM and other systems(See BU-211: Alternate Battery Systems)

Figure 1 shows a capacity drop from 100 percent to about 50 percent after the battery had been exposed to 700 micro cycles. The simulated start-stop test was performed in the Cadex laboratories. CCA remains high and only shows a decline after about 2,000 cycles.

**Figure 1: Capacity-drop of a starter battery in start-stop configuration [1]**
*The capacity drops to about 50 percent after 2 years of use. AGM battery is more robust.*

Test method:

The battery was fully charged and then discharged to 70% to resemble SoC of a micro hybrid in real life. The battery was then discharged at 25A for 40 seconds to simulate the engine off with the headlights on. To simulate cranking and driving, the battery was briefly discharged at 400A and then recharged. CCA was taken with the Spectro CA-12.

When connected in series, the voltage of each cell must be uniform, and this is especially important in large stationary battery systems. With time, individual cells fall out of line but applying an equalizing charge every 6 months or so should bring the cells back to similar voltage levels. (See BU-404: Equalizing Charge) What makes this service so difficult is providing the right remedy to each cell. While equalizing will boost the needy cells, the healthy cell gets stressed if the equalizing charge is applied carelessly. Gel and AGM batteries have lower overcharge acceptance than the flooded version and different equalizing conditions apply.

Flooded lead acid batteries are one of the most reliable systems and are well suited for hot climates. With good maintenance these batteries last up to 20 years. The disadvantages are the need for watering and good ventilation.

When VRLA was introduced in the 1980s, manufacturers claimed similar life expectancy to the flooded systems, and the telecom industry was enticed to switch to these maintenance-free batteries. By mid-1990 it became apparent that the life of VRLA did not live up to the flooded type; the typical service life of the VRLA is 5–10 years, less than half of the flooded equivalent. It was furthermore noticed that exposing VRLA batteries to temperatures above 40°C (104°F) could cause a thermal runaway due to dry-out.

North American Automotive Battery Failures

The 2005 failure-mode study was carried out by Douglas, East Penn., Exide Technologies and Johnson Controls. The sample battery pool included 2681 batteries tested between 2003 and 2004. The highlights include:

Battery life on average was 50 months. This is an improvement from earlier years that only had 41 months (2000) and 34 months (1962). Improved materials are prolonging battery life.
Northern and southern areas in North America deliver different life spans. Batteries in warmer climates die sooner than in cooler regions. See Figure 2.
Shorted cells and grid failures are the leading causes of battery failures in this survey.

**Figure 2: Failure mode as a function of region relating to temperature [2]**
*Batteries used in the northern area of North America last longer than those in the south.*

European Automotive Battery Failure

Figure 3 summarizes the failure-mode distribution of more than 800 AGM starter batteries carried out by Johnson Controls Power Solutions EMEA. The results were presented at AABC Europe 2017 in Mainz, Germany.

**Figure 3: Failure mode analysis in Europe [3]**
*The largest failure is mass wear-out as a function of usage reflecting in capacity fade and a rise of internal resistance.*

Table 1 summarizes the cause of failure derived from the JCI study.

Ratio	Cause	Diagnostics
47.8%	Mass wear-out, normal use	Loss of capacity, rise in resistance. Capacity estimation is most predictive
23%	Battery has low charge	Use voltmeter in open circuit when battery has rested
14.6%	No fault found	Better test methods puts these batteries back in service
12.5%	High internal resistance	Can be identified with battery testers measuring internal resistance
1.6%	Container damaged	Cannot be repaired in most cases
0.5%	Manufacturing defect	Manufacturers claim that most warranty causes are user induced.

Table 1: Cause of failure by percentage of over 800 AGM batteries at end-of-life

The above JCI study identifying end of battery life provides similar results to the test performed by a German luxury car maker in ca 2007 involving 175 starter batteries. In this test, heat failed batteries (high internal resistance) were eliminated and the results were plotted in Figure 4. The horizontal axis represents capacity; internal resistance correlating to CCA is on the vertical axis. CCA was measured according to DIN and IEC standards.

The end-of-life of most batteries occurs by passing through the Capacity Line located on the left of the green field in Figure 4. Very few batteries failed by dropping through the CCA Line. Capacity fade occurs through normal use mostly due to loss of active mass. Auxiliary power, such as start-stop, heating elements and mechanical door actions accelerate capacity loss. Increased internal resistance is a side effect of the active mass loss, but capacity estimation is the more reliable predictor of end-of-life. This is highlighted with the batteries sitting gray dot. Also see: BU-806: Tracking Battery Capacity and Resistance as part of Aging

**Figure 4: Capacity and CCA of 175 aging starter batteries**

Most batteries pass through the Capacity Line; few fail because of low CCA. The batteries were trunk mounted and driven in a moderate climate.

Note: Test was done by a German luxury car maker. Heat damaged batteries were eliminated.

Test Method: Capacity and CCA were tested according to DIN and IEC standards.

Comments

Some makers of battery testers claim to measuring capacity when only reading the internal resistance. Advertising features that lay outside of 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, but so does the user by poor cranking performance. See also BU-905: Testing Lead Acid Batteries

References

[1] Courtesy of Cadex, 2010
[2] Source: Survey carried out by Douglas, East Penn., Exide Technologies, and Johnson Controls
[3] Source: Johnson Controls Power Solutions EMEA at AABC Europe 2017 in Mainz, Germany

Last Updated: 2-Nov-2021

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