Lead-acid batteries have been used in cars for many years. They are the battery of choice for vehicles because they are able to discharge a large amount of power, which is necessary to get the starter motor to crank the engine. But how do they work?
Lead-acid batteries store and discharge electricity using lead plates that are submerged in an acid solution. The lead plates are grouped into cells with one positive and one negative plate separated by an insulating layer. There is a chemical reaction between the plates and the solution. During the reaction, electrons flow from the negative plate to the positive plate, creating an electric current.
One type of lead-acid rechargeable battery is the Sealed Lead Acid battery or SLA battery. It can also be called VRLA, which stands for Valve Regulated Lead Acid battery.
SLA batteries are the go-to choice for various applications like powering electronics in vehicles because they’re maintenance-free. Unlike flooded batteries, which are used in industrial applications, users don’t need to refill electrolyte solution. Additionally, you don’t need to worry about SLA batteries leaking their corrosive contents because they are built with shock-resistant and heat-resistant materials. They can also function fine in a wide range of temperatures, unlike other battery types. SLA batteries are also position-insensitive, which means you can put them in any position and they will function fine.
There are two main types of SLA batteries: AGM batteries and Gel Cell batteries. The difference between these two types is mainly within the technology that they use, particularly how the battery electrolyte is stored.
AGM stands for Absorbed Glass Mat. In this type of battery, the electrolyte is absorbed into fiberglass mat separators between the battery plates. AGM batteries also offer advantages like improved safety, better durability, and even resistance to freezing.
The electrolyte in gel batteries is suspended in a silica gel. This allows electrons to flow freely between the battery plates while preventing them from leaking out.
Overcharging is a risk for both AGM and gel cell batteries, but gel batteries are more vulnerable because overcharging can permanently damage the gel. As a result, gel batteries are less suitable for automotive use compared to AGM batteries.
AGM and Gell Cell batteries can have different internal lead plate thicknesses and active material densities, resulting in different characteristics when it comes to charging and discharging.
Batteries designed to supply power for extended periods are called deep cycle batteries. They are also designed to be charged and recharged repeatedly. Hence, they’re ideally used in marine vehicles like boats, submarines, as well as in golf carts and RVs.
Batteries that are designed to provide a rapid burst of power before needing to be recharged are called SLI batteries. SLI stands for starting, lighting, and ignition, which are processes that vehicles need. This is why SLI batteries are mainly used in automobiles.
There are also SLA batteries designed to handle the role of deep cycle and starter batteries called “dual purpose” batteries.
An SLA battery offers several perks over flooded batteries, which makes it the ideal type of lead acid battery for vehicles. First of all, SLA batteries are maintenance-free, as they don’t require you to regularly put water in the electrolyte solution. SLA batteries are also sealed, so you don’t have to worry about corrosive electrolytes spilling. In contrast to the traditional flooded lead-acid battery, which must always be upright, SLA batteries can be placed in any position. SLA batteries also have a low self-discharge rate, allowing their charge to last longer. Lastly, they are non-hazardous and can be shipped freely compared to flooded batteries.
A bad SLA battery can show several symptoms including the following:
A swollen, deformed battery indicates that it has exceeded its gassing voltage and has been overcharged. Overheating causes the battery to produce excess gas that it is unable to expel in time, causing the battery casing to expand.
At full charge, the resting voltage of a 12 Volt SLA battery should be around 12.6V. If it is lower, a battery cell might be failing. Check for hot spots on the battery’s side after a full charge cycle if you’re using a battery charger, as a failing cell can produce more heat.
When the battery overheats, it releases extra gas. As the gas enters the atmosphere outside the battery, it condenses, creating droplets on the battery’s surface (that makes it look like sweat).
Continuous overheating can cause the electrolyte level to drop and the battery to be damaged. Furthermore, the generated droplets are acidic and might damage the battery connections.
Depending on the type, an SLA battery can last between 300 and 1200 cycles. This largely varies depending on the battery trim. Cheaper trims last the shortest, while the most expensive battery trims last the longest. More expensive batteries also have better warranties.
We recommend batteries that are in the middle of the range, as they strike a good balance of value, reliability, and service life.
Nevertheless, A well-maintained gel or AGM battery can last for 7 years on average.
In practice, it is determined by how the battery is used, its operating temperatures, discharge cycle count, and charging method.
The self-discharge rate of a sealed lead acid battery is typically around 3.3 percent per month. It can be stored for up to 6 months without being charged, but this isn’t recommended.
Periodic recharging is required to ensure that the remaining capacity is not completely depleted and to prevent sulfation. Sulfation occurs when lead sulfate crystals harden on the battery plates, reducing the battery’s ability to recharge. Unused SLA batteries should be recharged every three months and stored in a cool, dry place with a temperature of 75oF (23oC) or less.
The vehicle’s alternator is responsible for charging the SLA battery. However, if your vehicle has remained unused for a very long time, then its SLA battery has probably discharged. You shouldn’t charge your battery using the alternator because it can overcharge and damage the battery. You need a special battery charger that provides the correct charge voltage. It’s also recommended to use a regulated battery charger that turns off automatically when the battery is full.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.