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) raise 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 five 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 temperature raise 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; in 2000 the life expectancy had been increased to 41 months. In 2010, BCI reports an average age of 55 months for starter batteries, of which the cooler North attains 59 months and the warmer South 47 months. Colloquial evidence in 2015 reveals that a battery kept in the trunk of a car lasts 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 a start-stop operation of a micro hybrid. It turns the IC engine off at a red traffic light and restarts it when the traffic flows again, resulting in about 2,000 micro-cycles per year. Data obtained from car manufacturers show a capacity drop to about 60 percent after two 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 flooded starter battery when micro cycling Start-stop function on a micro hybrid stresses the battery; the capacity drops to about 50 percent after two years of use. AGM is more robust for this application.
Courtesy of Cadex, 2010
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 and applying an equalizing charge every six 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 providing 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 for 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 40C (104F) could cause a thermal runaway due to dry-out.
Last updated 2016-01-17
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