What is the difference between GEL, AGM and Flooded batteries?
What is an AGM Battery?
An AGM battery, short for Absorbent Glass Mat battery, is a rechargeable battery that utilizes a fibreglass mat to absorb and contain the electrolyte, typically sulfuric acid. During the charging process, water molecules within the battery break down into hydrogen and oxygen gasses. The gasses are trapped by the porous fibreglass mat and subsequently recombined with the water. AGM batteries may also incorporate a one-way, pressure relief valve system to facilitate recombination. Because AGM batteries only contain enough electrolytes to keep the mat wet, they are light, spill-resistant, and safe.
What is a Flooded Battery?
A flooded battery, sometimes called a wet battery, is a traditional type of lead-acid battery that uses a liquid electrolyte, typically sulfuric acid. The electrolyte completely covers the lead positive and negative plates within the battery cells. Unlike AGM batteries, flooded batteries are not sealed and do not have special pressurized sealing vents. During the charging process, gasses produced at the positive plate are released through the vent plugs. As a result, flooded batteries require regular maintenance including adding distilled water to compensate for water loss during the charging process.
AGM vs Flooded Batteries
In this video case study, the choice between AGM, flooded, and lithium batteries for a material handling (ride-on order picker) application are discussed by Discover Battery’s VP of Business and Product Development Jimmy Au and Delta-Q Technologies’ Customer Success Manager Hiroshi Hasegawa:
When choosing between AGM and Flooded batteries, there are several important differences to be aware of.
Sealed vs Open Design: AGM batteries offer several benefits over flooded batteries due to their sealed design. First, AGM batteries are virtually maintenance-free. The electrolyte is absorbed into a fibreglass mat, eliminating the need for regular water additions. In contrast, flooded batteries require regular maintenance, including adding distilled water to compensate for water loss during the charging process, cleaning terminals, and ensuring proper ventilation.
Additionally, their sealed design allows AGM batteries to be installed in various orientations, offering flexibility and versatility in applications. Flooded batteries, on the other hand, must be installed upright. Because of their open design and the excess electrolytes they contain, they may spill if tipped or punctured, potentially causing damage or corrosion.
It is important to note that some brands of flooded or wet automotive batteries are also marketed and sold as sealed or maintenance-free. However, they are still flooded cell batteries. They do not have the same pressurized venting system as AGM batteries and will spill electrolytes if not kept upright.
Safety: Flooded batteries are not air transportable without special containers and they typically can’t be shipped via express courier or parcel post due to the risk of electrolyte spills. In contrast, AGM batteries have no DOT restrictions.
There are additional safety concerns when it comes to using flooded batteries around sensitive electronic equipment. The off-gassing can cause corrosion within the electrical circuits or other damage.
Cost: Although flooded batteries are typically less expensive upfront, they may end up costing more over the battery’s lifespan. This is due to the cost of regular maintenance including labour and service products, such as distilled water. Additionally, accidental spills and off-gassing during charging and discharging can lead to additional expenses and environmental concerns.
Performance: Flooded batteries are susceptible to acid stratification, which occurs when the heavier acid in the electrolyte separates from the water. This can cause premature battery degradation or failure. Acid stratification is accelerated by factors such as frequently operating in a partial state of charge, seldom receiving a full charge, being left unused for long periods, or even exposure to extreme temperatures. Acid stratification can also be caused by the battery being regularly micro-cycled between 3%-17.5% depth of discharge, high-cycled between 17.5% - 30% depth of discharge, or deep-cycled beyond 50% depth of discharge. This is especially true for the automotive starting type batteries and dual-purpose marine/RV combination cycling/starting batteries that many manufacturers are selling as low-cost alternatives to true deep cycle batteries.
AGM batteries are not affected by acid stratification to the same extent as flooded batteries. The fibreglass mat completely absorbs and constrains the acid which makes it more difficult for the acid to diffuse out of the water and accumulate at the bottom of the battery’s cells.
Figure 1 compares wet flooded vented battery gassing and VRLA DRY CELL AGM and GEL battery recombination.
Figure 1 - Vented Battery Gassing and VRLA DRY CELL Battery Recombination.
AGM and flooded batteries offer several distinct advantages and disadvantages. When selecting a battery, factors such as the specific application, desired lifespan, maintenance requirements, and budget should all be considered. For options that require frequent deep-cycle discharges, low maintenance, and improved performance, AGM batteries are often the preferred choice. However, for less demanding applications, and budget-conscious consumers, flooded batteries may still be a viable option.