When considering energy storage solutions, two widely known options usually come to mind: liquid (often referred to as conventional) batteries and AGM (adsorbed glass fiber) batteries. Both types of batteries perform the basic functions of energy storage, but there are significant differences in construction, maintenance, performance and applicability. In this blog post, we’ll dive into the basic differences between liquid and AGM batteries to help you make an informed decision based on your specific needs.
Liquid-Rich Batteries
Wet cells, also known as wet batteries, utilize a traditional design consisting of lead plates submerged in a liquid electrolyte solution. The lead plates are separated by bulkheads, so the electrolyte level must be monitored regularly and distilled water must be added periodically. These batteries typically require regular maintenance to ensure optimal performance and longevity.
For liquid-liquid flooded batteries, maintenance includes checking and maintaining proper fluid levels, adding distilled water when necessary, monitoring the specific gravity of the electrolyte, and performing periodic equalization charging to mitigate electrolyte stratification.
To maintain optimal performance, liquid-rich batteries require a specific charging regimen. The charge rate for these batteries is usually expressed as a percentage of battery capacity (C-rate). It is generally recommended that liquid-rich batteries be charged at less than 10% of their capacity. For example, a 100 amp-hour lead-acid battery should be charged at 10 amps or less. Charging at a slower current ensures a complete and thorough charge, allowing the electrolyte to mix effectively and minimizing the risk of stratification.
Typically, a 12V lead-acid battery has a high-capacity charge voltage of approximately 14.2 volts. This voltage is usually used during the high-capacity charging phase when the battery is being rapidly replenished. During this phase, the battery is stimulated by a constant current, which quickly restores energy. The elevated voltage promotes efficient electrochemical reactions within the battery. However, it is important to recognize that the specific high-capacity voltage may vary depending on the battery manufacturer, design, and temperature conditions.
Float charge voltage is typically around 13.4 volts. This float charge voltage represents the state in which the battery remains fully charged in standby or maintenance mode. During the float charge phase, the voltage is lower than during the high current charge phase. This voltage level has been specifically designed to ensure that the battery remains fully charged without the risk of overcharging or over-discharging. It compensates for self-discharge and any small loads connected to the battery, ensuring that the battery is always available.
AGM Batteries
AGM batteries have a sealed design with a fiberglass mat immersed in the electrolyte. The mat is cleverly placed between the lead plates to effectively hold the electrolyte in place. Due to this design, AGM batteries do not require refilling or checking of the electrolyte, eliminating the need for level-related maintenance.
AGM batteries have unique charging characteristics compared to liquid batteries. They typically follow a more controlled charging strategy.The recommended charge rate for AGM batteries is typically in the range of 10-25% of battery capacity. AGM batteries have a higher charge rate than liquid batteries due to the unique glass spacer design. This capability is attributed to reduced internal impedance and enhanced charge acceptance. The glass fiber separator holds the electrolyte firmly in place, preventing electrolyte spillage and excessive outgassing, which speeds up charging without compromising the integrity of the battery. To learn more about AGM technology, read our blog post The Complete Guide to AGM Batteries.
For 12V AGM lead-acid batteries, the high-current charging voltage is typically around 14.7 volts, while the float voltage is usually set at 13.8 volts.
When to Use Regular or AGM Batteries
When choosing between AGM (fiberglass barrier) batteries and regular batteries, consider the specific application, budget constraints, and charging requirements.
Application Requirements
Where cost is an important factor and regular maintenance is feasible, flow batteries are the best choice. They excel at handling high discharge rates and are capable of delivering higher inrush currents than AGM batteries. This makes them particularly suitable for high-power applications such as vehicle starting, off-grid renewable energy systems and heavy industrial machinery.
In contrast, AGM batteries are well suited for sealed, maintenance-free environments. Their low self-discharge rate allows them to hold a charge longer when not in use, which is beneficial for infrequent or seasonal applications. The fiberglass spacers in AGM batteries also provide excellent resistance to vibration and impact. Common applications include deep cycle storage for RVs and boats, backup power systems, renewable energy storage, and UPS (uninterruptible power supply) systems.
Budget Considerations
When choosing between the battery types listed above, it is critical to evaluate your budget. Liquid batteries require regular maintenance, such as checking and replenishing the electrolyte, equalizing the charge, and monitoring the specific gravity. This maintenance adds to the overall cost and effort of using liquid batteries. Conversely, while AGM batteries may have a higher initial cost, they offer convenience and durability, so long-term costs may be lower.
Charge Control
Consideration should also be given to the system’s charge control features.AGM batteries may require more advanced charge control features to avoid overcharging, whereas regular batteries can withstand higher charging voltages.
Are AGM batteries safer than liquid-rich batteries?
Liquid-rich batteries release gases such as hydrogen and oxygen during the charging and discharging cycles. Proper ventilation is essential to prevent the buildup of these potentially dangerous gases. In addition, the liquid electrolyte in a liquid-rich battery can cause leakage and corrosion if not handled properly.
On the other hand, AGM batteries have a gas recombination feature that recombines the gases produced during the charging process. This process significantly reduces harmful gas emissions, making AGM batteries a safer option for use in enclosed spaces. Their sealed design also eliminates the risk of electrolyte leakage and corrosion.
Summary
Regular and AGM batteries are two distinctly different types of lead-acid batteries, each with its unique advantages and considerations. Regular batteries require regular maintenance and fluid level checks, while AGM batteries require no maintenance. Regular batteries have a higher discharge rate, while AGM batteries offer convenience, safety, and superior vibration and shock resistance. Understanding these differences allows you to intelligently choose the right type of battery based on application needs, maintenance preferences, and safety considerations.