All About Battery Sulfation

When a battery is being discharged, the lead active material on the plates will react with the sulfate from the electrolyte, forming a lead sulfate on the plates. In other words, sulfation happens inside Lead-acid batteries when the electrolyte breaks down. As the sulphuric acid or the electrolyte splits, sulfur ions become free-forming crystals. These sulfur ion crystals then stick to the battery's lead plates, thus forming lead sulfate crystals. With time the crystals grow in size and become hard, covering the lead plates completely. This coverage deteriorates the overall efficiency and power storage capability of the battery. If left untreated, the sulfation process will only worsen the condition, and the user will lose their battery. 

When too much sulfation occurs, it can impede the chemical-to-electrical conversion and greatly impact battery performance.

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 an already fully charged battery in the form of a regulated current. Increasing the battery temperature to 50–60°C (122–140°F) during the corrective service 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. At this stage, no form of restoration seems possible.

Effects of Sulfation

When your battery has a buildup of sulfates, the following can happen:

• Longer charging times
• Excessive heat build-up
• Shorter running times between charges
• Dramatically shorter battery life
• Complete battery failure                                                                                                                                                                                                                                                                                                                                                                                                         

Causes of Sulfation

All lead-acid batteries will accumulate sulfation in their lifetime as it is part of the natural chemical process of a battery. But sulfation builds up and causes problems when

• Low electrolyte level – battery plates laid open to air will promptly sulfate.
• Batteries sit excessively long between charges. As little as 24 hours in a hot climate and a few days in a cooler climate. The longer a battery sits and is not recharged more sulphates develop on the plate.

Incorrect charging levels and settings. For example, undercharging of a battery to just 90% of the limit will permit sulfation of the battery utilizing the 10% of the battery not reactivated by not finishing the charging cycle.

Heavily Sulfated Plates (the white crystal/powder)

When there is no lead active material and or sulfate from the electrolyte remaining the battery then is completely discharged. After a battery reaches this state, it must be recharged. During recharge, the lead sulfate is reconverted into lead active material and the sulfate returned to the electrolyte.

If a battery is left in a discharged condition, the lead sulfate will harden and have a high electrical resistance, it is called a sulfated battery. The lead sulfate may become so hard that normal recharging will not break it down. Most charging sources, engine alternators, and battery chargers are voltage regulated. Their charging current is controlled by the battery's state of charge. During charging, the battery voltage rises until it meets the charger's regulated voltage, lowering the current output along the way.

When hard sulfate is present, the battery shows a false voltage higher than its true voltage, fooling the voltage regulator into thinking that the battery is fully charged. This causes the charger to lower its current output, leaving the battery discharged prematurely. Charging at a higher-than-normal voltage and low current may be necessary to break down the hardened sulfate.

Hardened sulfate also forms in a battery that is constantly being cycled in the middle of its capacity range (somewhere between 80% charged and 80% discharged), and is never recharged to 100%. Over time, a portion of the plate's active materials turns into hard sulfate. If the battery is continually cycled in this manner, it will lose more and more of its capacity until it no longer has enough capacity to perform the task for which it was intended. An equalizing charge, applied routinely every three to four weeks, should prevent the sulfate from hardening.

In both cases, the fact that the battery "won't take a charge" is a result of improper charging procedures, which allowed the sulfate to harden.

The best way to prevent sulfation is to practice proper battery maintenance and follow best practices in its upkeep.