How to Prolong Lead-acid Batteries
Explore what causes corrosion, shedding, electrical short, sulfation, dry-out, acid stratification and surface charge
A lead acid battery goes through three life phases: formatting, peak and decline (Figure 1). In the formatting phase, the plates are in a sponge-like condition surrounded by liquid electrolyte. Exercising the plates allows the absorption of electrolyte, much like squeezing and releasing a hardened sponge. As the electrodes activate, the capacity gradually increases.
Figure 1: Cycle life of a battery.
The three phases of a battery are formatting, peak and decline.
Courtesy of Cadex
Formatting is most important for deep-cycle batteries. They require 20–50 full cycles to reach peak capacity and field usage does this. During breaking-in, manufacturers recommend going easy on the battery. Starter batteries are less critical and do not need priming. The full cranking power is available from the beginning, although CCA will go up slightly with formatting in early use. (See also BU-701: How to Prime Batteries.)
A deep-cycle battery delivers 100–200 cycles before a gradual decline begins. Replacement should occur when the capacity drops to 70 or 80 percent. Some applications allow lower capacity thresholds but the time for retirement should never fall below 50 percent as aging may hasten once past the prime.
To keep lead acid in good condition, apply a fully saturated charge lasting 14 to 16 hours. If the charge cycle does not allow this, give the battery a fully saturated charge once every few weeks. If at all possible, operate at moderate temperature and avoid deep discharges; charge as often as you can. (See BU-403: Charging Lead Acid.)
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 5 years ago to 39 percent today. The report does not provide reasons for the larger wear and tear other than to assume that higher demands on the starter battery in modern cars induce added stress. The organization conducts a study every 5 years to determine the failure modes of batteries that have been removed from service. (BCI stands for Battery Council International.)
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. These conditions are found under: Corrosion, Shedding and internal Short, Sulfation and How to Prevent it, and Water Loss, Acid Stratification and Surface Charge. Most of these can be reduced by proper handling.
As battery care-giver, you have choices in how to prolong battery life. Each battery system has unique needs in terms of charging, depth of discharge and loading that should be observed. The following papers summarize what batteries like and dislike.
BU-415: How to Charge and When to Charge?
BU-706: Summary of Do’s and Don’ts
BU-806a: How Heat and Loading affect Battery Life