Primary Batteries (Non-Rechargeable / Disposable):

• Definition: These batteries are designed for single use. The electrochemical reactions that produce electricity are irreversible, or practically irreversible. Once the active chemical materials are consumed or depleted, the battery cannot be effectively recharged and must be disposed of.
• Examples: Alkaline batteries (e.g., AA, AAA for remote controls, flashlights), Zinc-Carbon batteries, Lithium-Metal batteries (used in some cameras, medical implants).
• Characteristics: Convenient for low-drain, intermittent use; typically have a good shelf life.

Secondary Batteries (Rechargeable):

• Definition: These batteries are designed to be recharged multiple times. The chemical reactions that occur during discharge can be reversed by applying an external electrical current (charging), restoring the battery's active materials and enabling it to store and release energy repeatedly.
• Examples: Lead-Acid, Nickel-Cadmium (Ni-Cad), Nickel-Metal Hydride (NiMH), Lithium-Ion (Li-Ion), Lithium-Polymer (Li-Po).
• Characteristics: Essential for applications requiring repeated energy storage and discharge cycles, offering long-term cost savings compared to primary batteries. This module focuses primarily on secondary batteries.

1. Lead-Acid Batteries:

• Chemistry: Composed of lead plates (the positive plate typically lead dioxide, the negative plate spongy lead) immersed in an electrolyte of dilute sulfuric acid.
• Operational Principle: During discharge, lead and lead dioxide react with sulfuric acid to form lead sulfate on both plates, consuming acid. During charging, this process is reversed, regenerating lead, lead dioxide, and sulfuric acid.
• Key Characteristics:
• Nominal Cell Voltage: Approximately 2 Volts per cell (e.g., a 12V battery has 6 cells in series).
• Cost-Effectiveness: Relatively inexpensive per unit of energy storage.
• Robustness: Mechanically robust and tolerant to overcharging (though excessive overcharging causes gassing).
• High Current Delivery: Excellent for high current applications (e.g., engine starting).
• Energy Density: Relatively low energy density (heavy and bulky for their energy capacity).
• Depth of Discharge (DoD): Sensitive to deep discharges; frequent deep discharges significantly reduce cycle life.
• Temperature Sensitivity: Performance degrades at low temperatures.
• Maintenance: Traditional flooded types require periodic watering. Sealed types like AGM (Absorbed Glass Mat) and Gel are maintenance-free.
• Applications: Automotive starter batteries (SLI), Uninterruptible Power Supplies (UPS), emergency lighting, alarm systems, electric wheelchairs, forklifts, solar power backup systems.

2. Ni-Cad (Nickel-Cadmium) Batteries:

• Chemistry: Uses nickel hydroxide for the positive electrode and cadmium for the negative electrode, with an alkaline electrolyte (potassium hydroxide).
• Operational Principle: Electrochemical reactions involve the transfer of electrons between nickel and cadmium compounds in the presence of the alkaline electrolyte during charge and discharge.
• Key Characteristics:
• Nominal Cell Voltage: 1.2 Volts per cell.
• Robustness: Extremely robust, tolerant to overcharge and overdischarge.
• Long Cycle Life: Very long cycle life (often 1000+ cycles) if properly managed.
• High Discharge Rates: Can deliver very high currents without significant voltage drop.
• Good Low-Temperature Performance: Performs well in cold environments.
• Memory Effect: A notable drawback where repeated partial discharge/recharge cycles can cause the battery to lose capacity.
• Toxicity: Cadmium is a toxic heavy metal.
• Applications: Power tools, portable radios, older laptops, medical equipment, remote control toys.

3. Li-Ion (Lithium-Ion) Batteries:

• Chemistry: Generally characterized by a positive electrode made of a lithium metal oxide, a negative electrode made of graphite, and a non-aqueous electrolyte. Lithium ions move between the electrodes during charge and discharge.
• Operational Principle: During discharge, lithium ions release electrons to the external circuit; during charging, this process reverses.
• Key Characteristics:
• Nominal Cell Voltage: Typically 3.2V to 3.7V, depending on chemistry.
• High Energy Density: Offers high energy storage per unit weight (lightweight).
• Low Self-Discharge Rate: Retains charge well.
• No Memory Effect: Can be charged/discharged at any point without losing capacity.
• Good Cycle Life: Typically 500-2000+ cycles.
• Safety Concerns: Susceptible to thermal runaway if mishandled.
• Cost: Generally more expensive than Lead-Acid.
• Applications: Dominant in consumer electronics, electric vehicles, grid-scale energy storage, power banks, cordless power tools.

Nominal Voltage (V): The average or typical voltage supplied by a battery cell or pack during its discharge cycle. It's the stated voltage for a battery (e.g., 12V, 3.7V). The actual voltage will vary slightly with charge level and load.

Capacity (Ah - Ampere-hour): The total amount of electrical charge (current over time) that a battery can deliver under specific conditions (e.g., temperature, discharge rate) before its voltage drops to a predefined cutoff point. A 100 Ah battery theoretically delivers 100 Amperes for 1 hour, or 10 Amperes for 10 hours.

• Calculation: Capacity (Ah) = Current (A) × Time (h).

C-rate: A standard way to express the rate at which a battery is discharged or charged relative to its maximum capacity.

• Definition: A 1C rate means that the current will discharge the entire battery in 1 hour. A 0.5C rate means the current will discharge it in 2 hours. A 2C rate means it takes 0.5 hours.
• Formula: Discharge Current (A) = C-rate × Capacity (Ah).

Depth of Discharge (DoD): The percentage or fraction of the battery's total capacity that has been discharged.

• Example: If a 100 Ah battery discharges 80 Ah, its DoD is 80%.
• Importance: For most secondary batteries, a shallower DoD significantly extends its cycle life.

Cycle Life: The total number of complete charge-discharge cycles a battery can undergo before its usable capacity drops to a specified percentage of its original capacity (e.g., 80%).

Purpose: To achieve a desired system voltage and/or total capacity that cannot be met by a single battery unit.

1. Series Connection:

• Method: The positive terminal of one battery is connected to the negative terminal of the next battery in a chain.
• Effect:
• Voltage: The total voltage of the battery bank is the sum of the nominal voltages of all individual batteries connected in series.
• Capacity: The total Ampere-hour (Ah) capacity of the battery bank remains the same as the capacity of a single battery in the series (assuming all batteries are identical).
• Purpose: To increase the overall operating voltage of the battery bank to match the load requirements.
• Example: Three 12V, 100Ah batteries connected in series will result in a 36V, 100Ah battery bank.

2. Parallel Connection:

• Method: All positive terminals of the batteries are connected together, and all negative terminals are connected together.
• Effect:
• Voltage: The total voltage of the battery bank remains the same as the nominal voltage of a single battery (assuming all batteries are identical).
• Capacity: The total Ampere-hour (Ah) capacity of the battery bank is the sum of the capacities of all individual batteries connected in parallel.
• Purpose: To increase the total current delivery capability and thus extend the backup time for a given load, or to provide higher peak currents.
• Example: Three 12V, 100Ah batteries connected in parallel will result in a 12V, 300Ah battery bank.

3. Series-Parallel Connection: A combination of both methods, used to achieve both a desired voltage level and a desired capacity.