Lead-acid batteries are the oldest rechargeable battery technology that is still widely used today. Invented by French physicist Gaston Planté in 1859, lead-acid batteries powered early electric vehicles and provided backup power for telegraph networks. While newer battery technologies have emerged, lead-acid batteries continue to be a popular choice for automotive and backup power applications due to their low cost, high surge current capability, and robustness.
Lead-acid batteries come in a variety of types, each suited for different applications. By understanding the different types of lead-acid batteries and their characteristics, users can select the optimal battery technology for their needs. This article provides an overview of the most common lead-acid battery types and their uses.
Flooded Lead-Acid Batteries
Flooded lead-acid batteries are the oldest and most widely used type of lead-acid battery. They are commonly found in automotive starter batteries and backup power supplies.
Flooded lead-acid batteries consist of lead plates immersed in a liquid electrolyte of sulfuric acid. As the battery discharges, the sulfuric acid reacts with the lead plates, forming lead sulfate. Charging the battery reverses this reaction, converting the lead sulfate back to lead on the battery plates.
Because the electrolyte is a liquid, flooded lead-acid batteries require maintenance to periodically check and replenish the electrolyte level. They also can spill electrolyte if tipped over. Vent caps allow gases produced during charging and discharging to escape the battery.
The flooded design has some advantages. Flooded batteries tend to have a low upfront cost. They can also provide high surge current for engine starting applications. However, they require more maintenance and emit hydrogen gas during charging that must be properly ventilated.
Common applications of flooded lead-acid batteries include automotive starting, lighting, and ignition (SLI) batteries, uninterruptible power supplies (UPS), electric golf carts, marine and RV power, and other deep cycle applications.
Valve-Regulated Lead-Acid (VRLA) Batteries
Valve-regulated lead-acid (VRLA) batteries, also known as sealed lead-acid batteries, retain the electrolyte within the battery casing and use pressure release valves to vent gases. The valve regulation allows VRLA batteries to be used in different orientations without leaking.
There are two main types of VRLA battery designs:
Absorbed Glass Mat (AGM): AGM batteries contain electrolyte that is absorbed into a fiberglass mat separator between the lead plates. This allows efficient recombination of gases into water during charging. AGM batteries are spillproof and can withstand vibration and shocks. They have excellent deep cycling capability and faster recharge times compared to flooded batteries. Common AGM applications include marine, RVs, golf carts, and backup power.
Gel Cell: Gel cell batteries contain a semi-solid electrolyte gel made of sulfuric acid mixed with silica powder and other additives. The thick gel limits electrolyte motion and provides resistance to vibration. Gel cells are low maintenance and can be operated in any orientation, but they have less deep cycling capability than AGM batteries. They are commonly used in wheeled mobility devices, solar power banks, and backup lighting.
Compared to flooded lead-acid, both AGM and gel cell VRLA batteries are higher in upfront cost. However, they are maintenance-free and operable in more positions, making them suitable for many applications where flooded batteries are impractical.
Lead-Carbon Batteries
Lead-carbon batteries are an advanced lead-acid chemistry that uses carbon additives in one or both of the battery plates. Adding carbon improves battery performance in several ways.
In lead-carbon batteries, a small amount of carbon is added to the negative plate. This reduces the growth of lead sulfate crystals during discharging, allowing faster recharging. It also reduces water loss, improving cycle life.
Some lead-carbon batteries also add carbon to the positive plate. This further reduces corrosion and water loss, boosting cycle life up to four times longer compared to conventional flooded batteries.
Other advantages of lead-carbon batteries include higher power density, improved charge acceptance under partial state of charge conditions, and better performance in partial state of health applications. Lead-carbon batteries have excellent deep cycling capability.
With their performance improvements, lead-carbon batteries are being adopted for microgrid energy storage, telecom backup power, residential solar storage, and other applications requiring deep cycling and frequent recharges. Despite the higher upfront cost, their long lifetimes improve total cost of ownership.
Lead-Crystal Batteries
Lead-crystal batteries represent an advancement over traditional lead-acid technology. They substitute lead oxide with an electrolytic manganese dioxide crystal cathode.
During discharge in a lead-crystal battery, the lead anode oxidizes while the manganese cathode gets reduced. This reaction occurs in reverse during charging. The manganese dioxide crystal structure has a high surface area that enables efficient reactions.
Compared to conventional lead-acid, lead-crystal batteries offer several advantages:
Higher voltage per cell of 2.4V to 2.5V, allowing higher system voltage configurations.
30-40% less energy loss during charging, improving efficiency.
Superior energy density and faster recharge capability.
Extended cycle life of over 1000 cycles at 80% depth of discharge.
Improved high temperature performance.
Due to these attributes, lead-crystal batteries are used in renewable energy storage, electric vehicles and other applications requiring high performance and frequent cycling. Their higher upfront cost can be justified by lower lifetime costs in cycling applications. Despite the superior performance, lead-crystal batteries have less market share than conventional lead-acid.
Lead-Calcium Batteries
Lead-calcium batteries offer an alternative grid alloy compared to traditional lead-antimony grids. In lead-calcium grids, a small amount of calcium is added to the lead.
The calcium addition offers a few key benefits:
Reduced water loss - Calcium reduces grid corrosion and self-discharge, cutting water consumption. This allows lower maintenance.
Longer life - With less corrosion, lead-calcium grids have greater longevity, especially in partial state of health service. Life can be 2-3 times longer than antimony grids.
Gas recombination - Lead-calcium grids promote faster oxygen recombination during charging, reducing water loss.
Reduced electrical resistance - Calcium improves conductivity, allowing higher discharge currents when needed.
On the other hand, lead-calcium batteries have less deep cycling capability than lead-antimony counterparts. The grids become more prone to sulfation and buckling with repeated cycling. Due to this downside, lead-calcium batteries are primarily used in standby power rather than cycling service.
Key applications of lead-calcium batteries include UPS systems, telecom backup, emergency lighting, and other stationary roles where long float life is needed but frequent deep cycling is not.
Conclusion
While lead-acid battery technology has been around for over 150 years, it continues to evolve. New lead-acid variants like VRLA, lead-carbon, lead-crystal and lead-calcium offer improvements in performance, lifetime, and versatility. Engineers can select the optimal lead-acid battery type based on their application requirements such as cycle life, maintenance, cost, and operating conditions. With their low cost and recyclability, lead-acid batteries will continue playing a key role in energy storage despite emerging battery chemistries.
