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Unlock your guides3.1 Lead-acid battery chemistry, design, and applications
3 min read•august 7, 2024
Lead-acid batteries are the oldest rechargeable battery technology, still widely used today. They come in two main types: flooded cell and (VRLA). Each has unique characteristics, making them suitable for different applications.
Lead-acid batteries have low energy density but are reliable and cost-effective. They're commonly used in automotive, UPS systems, and deep cycle applications. Understanding their chemistry, design, and performance is crucial for optimizing their use in various energy storage scenarios.
Lead-Acid Battery Types and Design
Flooded Cell and VRLA Batteries
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- Flooded cell lead-acid batteries contain liquid that can move freely within the battery case
- Require regular maintenance, including topping up the electrolyte level with distilled water
- Prone to spillage if not handled properly (stationary applications)
- Valve-regulated lead-acid (VRLA) batteries have a sealed design with a pressure relief valve
- Electrolyte is immobilized in a gel or absorbed in a glass mat (AGM)
- Maintenance-free and spill-proof, making them suitable for portable applications (UPS systems, wheelchairs)
- Higher cost compared to flooded cell batteries
Deep Cycle and Plate Design
- batteries are designed for repeated deep discharges (up to 80% depth of discharge)
- Thicker plates and higher active material density compared to starter batteries
- Used in applications requiring long-term energy storage (solar power systems, golf carts)
- Plate design affects battery performance and longevity
- Flat plates are simple and cost-effective but have limited surface area
- Tubular plates have higher surface area and improved but are more expensive to manufacture
- Grid alloys, such as lead-calcium and lead-antimony, influence battery characteristics
- Lead-calcium alloys reduce water loss and self-discharge but have lower cycle life
- Lead-antimony alloys improve deep cycling performance but increase water loss and maintenance requirements
Lead-Acid Battery Performance Characteristics
Energy Density and Self-Discharge
- of lead-acid batteries ranges from 30-50 Wh/kg
- Lower than other rechargeable battery technologies (Li-ion, NiMH)
- Limits their use in weight-sensitive applications (portable devices)
- Energy density of lead-acid batteries is approximately 60-110 Wh/L
- Requires larger battery sizes for high-energy applications (electric vehicles)
- of lead-acid batteries is relatively low, typically 3-5% per month at room temperature
- Increases with rising temperature and battery age
- Regular charging is necessary to maintain full capacity
Charge-Discharge Cycle and Sulfation
- of lead-acid batteries is around 70-80%
- Energy losses occur due to internal resistance and heat generation
- Proper charging algorithms (constant current-constant voltage) can optimize efficiency
- is a common failure mode in lead-acid batteries
- Occurs when lead sulfate crystals grow and accumulate on the plates during prolonged periods of low charge
- Reduces battery capacity and increases internal resistance
- Regular charging and occasional equalization charges can help prevent sulfation
Lead-Acid Battery Applications
Automotive and UPS Systems
- Automotive applications are the most common use for lead-acid batteries
- Starting, lighting, and ignition (SLI) batteries provide high current for engine starting
- Deep cycle batteries power electric vehicles (forklifts, golf carts)
- Low cost and reliable performance make them the preferred choice for vehicles
- Uninterruptible power supply (UPS) systems rely on lead-acid batteries for backup power
- Provide continuous power during utility outages to critical loads (data centers, hospitals)
- VRLA batteries are commonly used due to their maintenance-free and spill-proof design
- Long service life and high reliability are essential for UPS applications
Lead-Acid Battery Electrolyte
Electrolyte Composition and Concentration
- The electrolyte in lead-acid batteries is a mixture of sulfuric acid (H2SO4) and water
- Sulfuric acid is the active component that participates in the electrochemical reactions
- Water acts as a solvent and helps in ionic conductivity
- Electrolyte concentration, measured in terms of specific gravity, varies during charge and discharge
- Fully charged battery has a specific gravity of around 1.28
- Specific gravity decreases during discharge as sulfuric acid is consumed
- Electrolyte concentration affects battery performance and freezing point
- Higher concentration improves capacity but increases the risk of sulfation and decreases the freezing point
- Lower concentration reduces capacity but improves low-temperature performance
- Proper electrolyte maintenance, including regular specific gravity checks and adjustments, is crucial for optimal battery performance and longevity
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