How to Prolong Lead-acid Batteries

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 absorbing more liquid, much like squeezing and releasing a sponge. This enables the electrolyte to better fill the usable areas, which increases the capacity. Formatting is most important for deep-cycle batteries and requires 20 to 50 full cycles to reach peak capacity. Field usage does this and there is no need to apply added cycles for the sake of priming, however, manufacturers say 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.

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. Applying a fully saturated 14- to 16-hour charge and operating at moderate temperatures assure the longest service times. If at all possible, avoid deep discharges and charge more often.
The primary reason for the relatively short cycle life of a lead acid battery is depletion of 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 today. 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.Let’s look at the most common problems that develop with use and time — from internal to external — and what battery users can do to minimize the effect.

Corrosion / Shedding

Corrosion occurs primarily on the grid and is known as a softening and shedding of lead off the plates, a reaction that cannot be avoided because the electrodes in a lead acid environment are always reactive. Lead shedding is a natural phenomenon that can only be slowed down and not eliminated. A battery that reaches the end of life through this failure mode has met or exceeded the anticipated life span. Limiting the depth of discharge, reducing the cycle count, operating at a moderate temperature and controlling overcharge are key in keeping corrosion in check. To reduce corrosion on long-life batteries, manufacturers keep specific gravity at a moderate 1.200 when fully charged. This, however, reduces the capacity the battery can hold.
Applying prolonged overcharge is another contributor to grid corrosion. This is especially damaging to sealed lead acid systems. While the flooded lead acid has some resiliency to overcharge, sealed units must operate at a correct float charge. Chargers with variable float voltages that adjust to the prevailing temperature help to keep grid corrosion in check. Such chargers are in common use for stationary batteries.
To attain maximum surface area, the lead on a starter battery is applied in a sponge-like form. With time and use, chunks of lead fall off and reduce the performance. The thicker plates prevent this from happening on deep-cycle batteries. Figure 2 illustrates the innards of a corroded lead acid battery.

Figure 2: Innards of a corroded lead acid battery Grid corrosion is unavoidable because the electrodes in a lead acid environment are always reactive. Lead shedding is a natural phenomenon that can only be slowed and not eliminated. Courtesy of Journal of Power Sources (2009)

The terminals of a battery can also corrode, and this is often visible in the form of white powder. The phenomenon is a result of oxidation between two different metals connecting the poles. Terminal corrosion can eventually lead to an open electrical connection. Changing the connecting terminals to lead, the same material as the battery pole of a starter battery, will solve most corrosion problems.

Short

The term “short” is commonly used to describe a general battery fault when no other definition is available. As the colloquial term “memory” was the cause of all battery ills in the NiCd days, so do we today describe non-functioning lead acid batteries simply as being “shorted.” Let’s take a closer look and see what a shorted lead acid battery truly is.
The lead within a battery, especially in deep-cycle units, is mechanically active and when a battery discharges, the lead sulfate causes the plates to expand. This movement reverses during charge and the plates contract. The cells allow for some expansion but over time the growth of large sulfite crystals can result in a soft short that increases self-discharge. This mechanical action also causes shedding of the lead material. On a starter battery, the shedding is manageable because the lead plates are thin and the battery does not go through a deep discharge. On a deep-cycle battery, on the other hand, shedding is a major concern.
As the battery sheds its lead to the bottom of the container, a conductive layer forms, and once the contaminated material fills the allotted space in the sediment trap, the now conductive liquid reaches the plates and creates a shorting effect. The term “short” is a misnomer and elevated self-discharge would be a better term to describe the condition.
“Soft shorts” are difficult to detect because the battery appears normal immediately after a charge and everything seems to function as it should. In essence, the charge has wiped out all evidence of a soft short, except perhaps an elevated temperature on the housing. Once rested for 6–12 hours, the battery begins to show anomalies such as a lower open-circuit voltage and reduced specific gravity. The measured capacity will also be low because self-discharge has consumed some of the stored energy. According to the 2010 BCI Failure Modes Study, shorted batteries accounted for 18 percent of battery failures, a drop from 31 percent five years earlier. Improved manufacturing methods may account for this reduction.
Another form of “soft” short is mossing. This occurs when the separators and plates are slightly misaligned as a result of poor manufacturing. This causes parts of the plates to become naked. The exposure promotes the formation of conductive crystal moss around the edges, which leads to elevated self-discharge.
Lead dropis another cause of short, in which large chunks of lead break loose from the welded bars connecting the plates. Unlike a “soft” short that develops with wear-and-tear, a lead drop often occurs early in battery life and causes a more serious short that is associated with a permanent voltage drop. The shorted cell has no charge and the specific gravity of the electrolyte is close to 1.00. This is mostly a manufacturing defect and cannot be repaired.
The most radical and serious form of short is a mechanical failure in which the suspended plates become loose and touch each other. This results in a sudden high discharge current that can lead to excessive heat buildup and thermal runaway. Sloppy manufacturing as well as excessive shock and vibration are the most common contributors to this failure.

Sulfation

Sulfationoccurs when a lead acid battery is deprived of a full charge. This is common with starter batteries in cars that are driven in the city with load-hungry accessories engaged. A motor in idle or at low speed cannot charge the battery sufficiently.
Electric wheelchairs have a similar problem in that the users might not charge the battery long enough. An eight-hour charge during the night when the chair is free is not enough. Lead acid must periodically be charged 14–16 hours to attain full saturation. This may be the reason why wheelchair batteries last only two years, whereas golf car batteries deliver twice the service life. Longer leisure time allows golf car batteries to get a fully saturated charge.
Solar cells and wind turbines do not always provide sufficient charge, and lead acid banks succumb to sulfation. This happens in remote parts of the world where villagers draw generous amounts of electricity with insufficient renewable resources to charge the batteries. The result is a short battery life. Only a periodic fully saturated charge could solve the problem, but without an electrical grid at their disposal, this is almost impossible. An alternative is using lithium-ion, a battery that is forgiving to a partial charge, but this would cost much more than lead acid.
What is sulfation? During use, small sulfate crystals form, but these are normal and are not harmful. During prolonged charge deprivation, however, the amorphous lead sulfate converts to a stable crystalline that deposits on the negative plates. This leads to the development of large crystals, which reduce the battery’s active material that is responsible for high capacity and low resistance Sulfation also lowers charge acceptance; with sulfation charging will take longer.
There are two types of sulfation: reversible or soft sulfation, and permanent or hard sulfation. If a battery is serviced early, reversible sulfation can often be corrected by applying an overcharge to a fully charged battery in the form of a regulated current of about 200mA. The battery terminal voltage is allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on a 12V mono block) for about 24 hours. Increasing the battery temperature to 50–60°C (122–140°F) further helps in dissolving the crystals. Permanent sulfation sets in when the battery has been in a low state-of-charge for weeks or months, and at this stage no form of restoration is possible.
There is a fine line between reversible and non-reversible sulfation, and most batteries have a little bit of both. Good results are achievable if the sulfation is only a few weeks old; restoration becomes more difficult the longer the battery is allowed to stay in a low SoC. A battery may improve marginally when applying a de-sulfation service but it may not reach a satisfactory performance level. A subtle indication of whether a lead acid can be recovered is visible on the voltage discharge curve. If a fully charged battery retains a stable voltage profile on discharge, chances of reactivation are better than if the voltage drops rapidly with load.
Several companies offer anti-sulfation devices that apply pulses to the battery terminals to prevent and reverse sulfation. Such technologies tend to lower sulfation on a healthy battery but they cannot effectively reverse the condition once present. Manufacturers offering these devices take the “one size fits all” approach and the method is unscientific. A random service of pulsing or overcharging can harm the battery in promoting grid corrosion. Technologies are being developed that measure the level of sulfation and apply a calculated overcharge to dissolve the crystals. Chargers featuring this technique only apply de-sulfation if sulfation is present and for only a short duration as needed

Water Loss / Dry-out

During use, and especially on overcharge, the water in the electrolyte splits into hydrogen and oxygen. The battery begins to gas, which results in water loss. In flooded batteries, water can be added but in sealed batteries water loss leads to an eventual dry-out and decline in capacity. Water loss from a sealed unit can eventually cause disintegration of the separator. The initial stages of dry-out can go undetected and the drop in capacity may not immediately be evident. Early detection of this failure is important. 
On overcharge, a battery becomes a water-splitting device that turns water into oxygen and hydrogen. The fuel cell does the opposite; it turns oxygen and hydrogen back to electricity and produces water. Turing water to hydrogen needs energy; converting hydrogen and oxygen to water generates energy. Read more about Fuel Cell Technology.

Acid Stratification

Theelectrolyte of a stratified battery concentrates on the bottom, starving the upper half of the cell. Acid stratification occurs if the battery dwells at low charge (below 80 percent), never receives a full charge and has shallow discharges. Driving a car for short distances with power-robbing accessories contributes to acid stratification because the alternator cannot always apply a saturated charge under such conditions. Large luxury cars are especially prone to this. Acid stratification is not a battery defect per se but the result of a particular usage. Figure 3 illustrates a normal battery in which the acid is equally distributed from top to bottom.

Figure 3: Normal battery The acid is equally distributed from the top to the bottom of the battery, providing good overall performance. Courtesy of Cadex

Figure 4 shows a stratified battery in which the acid concentration is light on top and heavy on the bottom. The light acid on top limits plate activation, promotes corrosion and reduces the performance, while the high acid concentration on the bottom makes the battery appear more charged than it is and artificially raises the open-circuit voltage. Because of unequal charge across the plates, the CCA performance is also affected.

Figure 4: Stratified battery The acid concentration is light on top and heavy on the bottom. This raises the open circuit voltage and the battery appears fully charged. Excessive acid concentration induces sulfation on the lower half of the plates. Courtesy of Cadex

Allowing the battery to rest for a few days, doing a shaking motion or tipping the battery on its side helps correct the problem. Applying an equalizing charge by raising the voltage of a 12-volt battery to 16 volts for one to two hours also helps by mixing the electrolyte through electrolysis. Avoid extending the topping charge beyond its recommended time.

Acid stratifications cannot always be avoided. During cold winter months, starter batteries of passenger cars dwell at a 75 percent charge level. Knowing that motor idling and driving in gridlocked traffic does not sufficiently charge the battery, a charge with an external charger may be needed from time to time. If this is not practical, a switch to an AGM battery will help. AGM does not suffer from acid stratification and is less subject to sulfation if undercharged than the flooded version. AGM is a little more expensive than the flooded starter battery.

Surface Charge

Lead acid batteries are sluggish and cannot convert lead sulfate to lead and lead dioxide quickly enough during charge. As a result, most of the charge activities occur on the plate surfaces. This induces a higher state-of-charge on the outside than in the inner plate. A battery with surface charge has a slightly elevated voltage. To normalize the condition, switch on electrical loads to remove about one percent of the battery’s capacity, or allow the battery to rest for a few hours. Surface charge is not a battery defect but a reversible condition resulting from charging.

Simple Guidelines for Extending Battery Life

• Charge in a well-ventilated area. Allow a fully saturated charge of 14 hours.
   
• Always keep lead acid charged. Avoid storage below 2.10V/cell, or SG below 1.190.
   
• Avoid deep discharges. The deeper the discharge, the shorter the battery life will be. A brief charge on a 1- to 2-hour break during heavy use prolongs battery life.
   
• Never allow the electrolyte to drop below the tops of the plates. Exposed plates sulfate and become inactive. When low, add only enough water to cover the exposed plates before charging; fill to the correct level after charge.
   
• Never add acid; use distilled or ionized water. Tap water may be usable in some regions.
   
• When new, a deep-cycle battery may only have about 75 percent capacity. Formatting as part of field use will gradually increase performance. Apply a gentle load for the first five cycles to allow a new battery to format.