Lead Acid, AGM, and Gel-Cell Batteries

Flooded lead-acid batteries are what you typically find in a gasoline powered car. Invented in 1859 the old wet cell lead acid battery has been with us for a long time. Lead-acid batteries are cheap to manufacture, flexible in their application, have a predictable lifespan and can be recycled. By the 1920s people were tired of having to manually crank start their automobiles. Many people broke their wrists and thumbs trying to get their car started. The first electric start car was introduced by Cadillac which utilized a lead acid battery and an electric start motor.

The fluid in a lead acid battery is called electrolyte, a mixture of sulphuric acid and water. Flooded lead-acid batteries require regular maintenance by adding distilled water. These batteries operate by producing an electric charge when the sulphate in the sulphuric acid becomes bonded to the lead in the battery. The electrical charge is replenished by reversing this reaction resulting in the sulphate going back into sulphuric acid.

When your battery charges, the electrolyte heats up and some of the water evaporates. During a process called electrolysis, the water breaks down into hydrogen and oxygen gases that dissipate. The level of electrolyte becomes lower in the battery and it becomes necessary to add some distilled water until the proper level is restored. The electrolyte should cover the battery plates.

Modern sealed "maintenance free" batteries do not have removable caps allowing you to replenish lost electrolyte. Although electrolyte is lost over time due to some venting, very little is lost in comparison to traditional batteries. A special calcium alloy of lead is utilized in maintenance-free batteries to sustain the water for an extended period. When a maintenance-free battery starts to lose its capacity to hold a charge, it’s better to replace it with a new one. Whereas, in the case of conventional batteries, you can add distilled water to recover electrolytes in plates.

Most of the time when you purchase a modern Maintenance Free battery it will be an AGM battery. An AGM battery is a 12-volt car battery that can be used as an alternative to traditional flooded lead-acid batteries. The Valve Regulated Lead-acid batteries include AGM and gel technology. These are also known as SLA.

The AGM battery and the standard lead acid battery are technically the same when it comes to their base chemistry. They both use lead plates and an electrolyte mix of sulfuric acid and water and have a chemical reaction that produces hydrogen and oxygen as a byproduct. The flooded lead acid battery (FLA battery) uses lead plates submerged in liquid electrolyte.

In a conventional FLA battery the gases produced during its chemical reaction are vented while the AGM is a sealed battery, there’s minimal to no vented gasses. Gases produced during the chemical reaction in an AGM battery are recombined with the electrolyte. The AGM battery is maintenance-free and can be placed in more enclosed areas such as vehicles with batteries in trunks and under seats.

AGM

AGM is an acronym for Absorbent Glass Material. AGM batteries hold and suspend the electrolyte mixture like a sponge with tiny glass fibers while maintaining evenly distributed contact with the active lead materials on the plates. The electrons flow in a series circuit through six cells, each of which runs at approximately 2 volts for a total of 12 volts.

The AGM battery tends to be built harder than the flooded lead acid battery, as it originally served military and aviation use. Due to their design they are shock and vibration resistant.

The AGM battery’s internal resistance is among the lowest of the various lead acid batteries. While a new flooded lead acid battery can have an internal resistance of 10-15%, a new AGM battery can be as low as 2%. Low internal resistance translates to increased battery voltage output. It also means a reduced loss of heat as power circulates in the system.

AGM batteries have an 80% depth of discharge (DoD), which is better than the 50% DoD offered by a flooded cell battery. This makes the AGM battery well-suited to deep cycle applications. Depth of Discharge indicates how much battery capacity can be discharged safely without damaging it.

Charging: The charging voltages are the same as for any standard battery, there is no need for any special adjustments or problems with incompatible chargers or charge controls. However, AGM batteries are sensitive to overcharging and undercharging and improper charging can reduce overall capacity. You can buy battery chargers with a AGM setting that is better suited to these batteries. It is recommended to use a battery charger designed for AGM batteries.

AGM batteries improve on a major flaw of flooded batteries, spillage.

The AGM lead-acid batteries will be labeled as AGM, or Absorbed Glass Mat, or dry cell, sealed regulated valve, non-spillable, or valve-regulated on the label. AGM batteries are also called starved electrolyte’, or membrane batteries.

Gel-Cell

Gel batteries use a different method to keep the electrolyte in place. Gel batteries typically use a chemical agent such as silica to create a gel-like substance that allows for less movement. Both gel and AGM batteries are considered Valve-Regulated Lead-Acid (VRLA) batteries. The electrolyte in Gel batteries have a look of jelly.

Charging: Never charge a gel cell battery with a conventional lead acid battery charger. These batteries are finicky and are easily destroyed by improper charging. They must be charged at a slower rate(C/20) to prevent excess gas from damaging the cells. These batteries are never to be "fast charged."

Gel-filled lead-acid batteries come with a Geld filled’ label on the battery.

Comparison AGM and Gel

There are a number of similarities between AGM and Gel batteries. There is greater flexibility in how they can be installed and mounted, even laying sideways in some devices such as portable jump starters.

Comparing AGM to Gel Batteries:

• The gel batteries can work in warmer temperatures, while AGM batteries work efficiently in cold temperatures.
• According to the depth of discharge, temperature, maintenance, and how often and how deep cycled, the lifespan of agm batteries is around 4 to 8 years and gelled deep cycle battery is around 2 to 5 years.
• AGM batteries are less expensive than gel batteries
• AGM batteries can be discharged at a higher rate than gel batteries
• AGM batteries are typically lighter than gel batteries
• Gel batteries last longer and are made with thicker plates
• Gel batteries are less sensitive to temperature than AGM batteries
• Gel batteries are less likely to leak than AGM batteries

Terminology

Flooded Lead Acid: The flooded lead acid battery (FLA battery) is the most common lead acid battery type and is often referred to as a standard or conventional, or even a wet cell battery.

Sealed Lead Acid: Also known as VRLA or Valve Regulated Lead Acid battery. These are Flooded Lead Acid batteries that uses a one-way valve to regulate pressure resulting from internal chemical reactions. You can not perform maintenance on these batteries by adding additional liquid electrolyte or water.

Deep Cycle: The deep cycle battery is designed to deliver steady power over an extended period of time rather than a lot of amps for a quick moment such as starting a car. Marine vehicles and computer backup units utilize deep cycle batteries. These batteries can be any of the types of lead acid including AGM and gel, or even Lithium.

EFB: Enhanced Flooded Lead Acid Battery is a flooded battery designed as an improvement over conventional batteries that’s also cheaper than an AGM battery.

Lithium: Not yet that suitable for cars and trucks, Lithium batteries are now being used for motorcycles, ATVs, and other similar vehicle types. These are not the type of lithium-ion batteries in your phone but are constructed from a lithium-iron-phosphate blend that slightly reduces its power density for significantly more chemical stability. Lithium batteries produce 13.2 volts rather than 12v.

Timeline

1859 - French physician Gaston Planté invented a rudimentary lead-acid battery

1912 - Cadillac introduced the first gasoline passenger car with electric start invented by Charles Kettering

1953 - Auto manufacturers started the transition from 6v to 12v