Everything You Need to Know About Rechargeable Batteries

11 Battery Charging and Discharging Parameters

1. Voltage: Voltage is the electrical potential difference between the positive and negative terminals of a battery. It’s the driving force that pushes current through a circuit, and it’s one of the most fundamental parameters to understand.

• Nominal Voltage: This is the average voltage during discharge. For example, a lithium-ion battery typically has a nominal voltage of 3.7V.
• Fully Charged Voltage: When fully charged, the voltage reaches its peak. For a LiPo battery, this is usually 4.2V.
• Discharged Voltage: This is the minimum voltage before the battery is considered empty. For most LiPo batteries, this is around 3.0V.

2. Capacity, measured in milli ampere-hours (mAh), indicates how much energy a battery can store. Think of it as the size of the battery’s fuel tank.

• Theoretical Capacity: This is the total energy the battery can store under ideal conditions.
• Actual Capacity: In real-world scenarios, the usable capacity is often lower due to inefficiencies like heat loss and internal resistance.

3. The charge/discharge rate, or C-rate, defines how quickly a battery can be charged or how quickly a battery can safely deliver energy/discharge. It’s expressed as a multiple of the battery’s capacity.

• 1C Charge Rate: Charging/ Discharge a 2000mAh battery at 2000mA (1 × capacity).
• 2C Charge Rate: Charging/ Discharge the same battery at 4000mA (2 × capacity).
  

4. Cycle life refers to the number of charge-discharge cycles a battery can undergo before its capacity drops to a specified percentage (usually 80% of its original capacity).

• Typical Cycle Life: 300–500 cycles for LiPo batteries.
• Factors Affecting Cycle Life: Depth of discharge, charging speed and operating temperature.
  

5. Internal resistance (IR) is the resistance within the battery that opposes the flow of current. It’s measured in milliohms (mΩ).

• Low Internal Resistance: Allows higher discharge rates and better performance.
• High Internal Resistance: Reduces efficiency and causes heat buildup.
  

6. The self-discharge rate is the rate at which a battery loses energy when not in use.

• Typical Self-Discharge Rate: 1–5% per month for lithium-ion batteries.
• Factors Affecting Self-Discharge: Temperature and battery age.

7. State of charge (SoC) indicates how much energy is left in the battery as a percentage of its total capacity.

• 100% SoC: Fully charged.
• 0% SoC: Fully discharged.

8. Depth of discharge (DoD) indicates how much of the battery’s capacity has been used.

• Shallow Discharge: Using only 20–30% of the battery’s capacity.
• Deep Discharge: Using 80–100% of the battery’s capacity.

9. Operating temperature refers to the range of temperatures within which a battery can safely function.

• Typical Range: 0°C to 45°C for charging, -20°C to 60°C for discharging.
• Effects of Extreme Temperatures: Reduced performance, swelling, or even fire.

10. Battery State of Health (SoH) tells how good a battery is. It shows how much life the battery has left. SoH compares the battery’s current condition to when it was new. If a battery has 80% SoH, it can only hold 80% of the charge it could when it was new. This helps you know if the battery needs replacing soon.

11. Typical charging voltages

• Bulk Charge: Bulk charge is the first and fastest stage of battery charging, where a constant and maximum safe current is supplied to the battery to quickly bring it to about 80-90% of its capacity (14.4V to 14.7V for a 12V system).
• Float Charge: The constant voltage applied to a battery to keep it fully charged after it has reached its maximum capacity without overcharging (typically 13.0V-13.8V for a 12V system).
• Equalizing Charge: The equalizing charge is a controlled overcharge performed periodically on flooded lead-acid batteries only. It involves raising the voltage above the normal absorption level (e.g., to 15-16V for a 12V system) for a limited time to applied to a battery to balance the voltage of individual cells, break up sulfate deposits, to compensate for temperature differences and to recover from deep discharge.

Note: Equalization charging is generally not recommended for sealed AGM or Gel-type batteries, as it can cause permanent damage due to excessive gassing they cannot safely vent.