A lead acid battery goes through three life phases, called formatting, peak and decline (Figure 1). In the formatting phase, try to imagine sponge-like lead plates that are being exposed to a liquid. Exercising the plates allows the absorption of more liquid, much like squeezing and releasing a sponge. This enables the electrolyte to better fill the usable areas, an exercise that increases the capacity.
Formatting is most important for deep-cycle batteries and requires 20 to 50 full cycles to reach peak capacity. Field usage achieves this. There is no need to apply added cycles for the sake of priming; however, manufacturers recommend to go easy on the battery until broken in. Starter batteries are less critical and do not need priming; the full cranking power is present right from the beginning, although the CCA reading will go up slightly with early use.
Figure 1: Cycle life of a battery
The three phases of a battery are formatting, peak and decline.
Courtesy of Cadex
A deep-cycle battery delivers 100–200 cycles before it starts the gradual decline. Replacement should occur when the capacity drops to 70 or 80 percent. Some applications allow lower capacity thresholds but the time for retirement should not fall below 50 percent because the aging occurs rapidly once the battery is past its prime. Apply a fully saturated charge of 14 to 16 hours. Operating at moderate temperatures assure the longest service times. If at all possible, avoid deep discharges; charge more often.
The primary reason for the relatively short cycle life of a lead acid battery is depletion of the active material. According to the 2010 BCI Failure Modes Study,* plate/grid-related breakdown has increased from 30 percent five years ago to 39 percent. The report does not give reasons for the increased wear-and-tear, other than to assume that higher demands of starter batteries in modern cars induce added stress.
While the depletion of the active material is well understood and can be calculated, a lead acid battery suffers from other infirmities long before plate- and grid-deterioration sound the death knell. The following articles address the most common problems that develop with use and time and what battery users can do to minimize the effect.
* Every five years, the Battery Council International Technical Subcommittee conducts a study to determine the failure modes of batteries that have been removed from service.