12 Ways Lithium Battery Charging & Discharging Explained With Curve

Key takeaways

• CC-CV charging is the standard method used for most lithium-ion batteries
• Constant current (CC) charges the battery quickly at the beginning
• Constant voltage (CV) safely completes charging and protects battery life
• The transition between CC and CV defines the lithium-ion charging curve
• Constant current discharge is commonly used to evaluate battery performance
• Understanding battery discharge curves helps predict runtime and system behavior

Part 1. 5 Types of lithium battery charging methods: CC, CV, CC-CV, CP, CP-CV

In addition to the CC-CV charging method required by the standard, lithium batteries can also be charged by CC, CV, CP, CP-CV, etc.

1. What is Constant Current (CC) Charging?

Figure 1: Constant current charging curve

During the constant current charging stage, the charger delivers a fixed current — for example, 1A, 2A, or higher depending on battery specifications.

At this point:

• The battery voltage gradually increases
• Charging is relatively fast
• Heat generation remains controlled

This is the phase where your battery gains most of its capacity. In fact, many lithium batteries reach 60–80% capacity during constant current charging.

Imagine charging an electric scooter battery. At the beginning, energy flows quickly. The battery is “hungry,” and the charger pushes current steadily. Everything seems fast and efficient.

But then something changes.

As the battery fills up, its internal resistance increases. Continuing constant current charging would push the voltage too high. That’s where constant voltage charging begins.

How to Read Lithium Battery Discharge Curve and Charging Curve?

2. What is Constant Voltage (CV) charging?

Figure 2: Constant voltage charging curve

Once the battery reaches its maximum voltage — typically 4.2V for standard lithium-ion cells — the charger switches to constant voltage charging.

Now, instead of controlling current, the charger holds voltage steady.

At this stage:

• Current gradually decreases
• Charging slows down
• Battery protection becomes the priority

This is why the last 20% of charging always feels slower. You’re in the CV phase.

This part may feel inefficient, but it’s actually essential. The CV phase helps balance cells, reduce stress, and extend battery lifespan.

Without constant voltage charging, lithium batteries would degrade much faster.

2.1) Cc vs cv charging: what’s the difference?

Understanding the cv vs cc charging difference is easier when you compare them side-by-side.

This cv and cc difference explains why lithium batteries rely on both stages. One provides speed, the other provides safety.

In other words, constant current gets you there fast, constant voltage gets you there safely.

3. What’s CC-CV (Constant Current – Constant Voltage) Charging?

Figure 3: Constant current constant voltage charging curve

CC CV charging (constant current–constant voltage charging) is the standard charging method for lithium-ion batteries. Instead of charging with one fixed parameter, the charger switches between two phases.

At first, the charger delivers constant current. This quickly pushes energy into the battery. Then, once the battery voltage reaches a set limit, the charger switches to constant voltage mode, gradually reducing current until charging completes.

This approach balances three important goals:

• Fast charging
• Safety
• Battery lifespan

If you only used constant current, you’d risk overheating. If you only used constant voltage, charging would take far too long. CC-CV charging finds the middle ground.

This is why you’ll see cc cv charging used in everything from smartphones to electric vehicles.

3.1) Lithium battery cc cv charging curve

Figure 3: Constant current constant voltage charging curve

If you plot cc and cv battery charging on a graph, you’ll see a distinctive shape.

At first, voltage climbs steadily while current remains flat. Then, voltage stabilizes while current drops gradually. This creates the classic CC-CV charging curve.

This curve is widely used in battery engineering to:

• Evaluate charger design
• Analyze battery health
• Compare battery chemistries

Understanding this curve also helps explain why fast charging becomes slower near full capacity. The system intentionally reduces current to protect the battery.

3.2) Why lithium batteries use cc cv charging

Lithium batteries are sensitive to overvoltage and overheating. Unlike older chemistries, they require precise charging control.

CC-CV charging works well because it:

• Minimizes battery stress
• Reduces overheating risk
• Improves cycle life
• Maintains stable performance

Over time, this charging method has become the industry standard for lithium-ion batteries.

And once you understand how cc cv charging works, it becomes much easier to read datasheets, interpret battery discharge curves, and design better battery systems.

4. Constant Power (CP) Charging

Figure 4: Constant power charging curve

Constant Power (CP) charging involves delivering a fixed amount of power to the battery, where both current and voltage adjust to maintain the target power output.

• How it works: The charger dynamically adjusts both current and voltage to ensure that a constant power level (measured in watts) is delivered to the battery throughout the charging process. This method can be particularly useful when the battery’s voltage and current need to be optimized together for power-based applications.
• Why it’s used: CP charging is less common but can be used in applications requiring steady power delivery, like certain types of energy storage systems or high-power devices.
• Risks: One challenge of CP charging is ensuring that both the current and voltage stay within safe limits for the battery. Excessive current or voltage could damage the battery if not controlled carefully.

5. CP-CV (Constant Power – Constant Voltage) Charging

Figure 5: Constant power constant voltage charging curve

CP-CV is a hybrid charging method that begins with constant power (CP) charging and then switches to constant voltage (CV) charging as the battery approaches full charge.

• CP phase: Initially, the charger applies constant power, adjusting both current and voltage to maintain the desired power output.
• CV phase: As the battery reaches its voltage limit, the charger switches to constant voltage mode and reduces the current to prevent overcharging.
• Why it’s used: CP-CV charging is useful for applications where maintaining a fixed power input is critical, such as in some industrial or renewable energy systems. The shift to CV ensures that the battery isn’t overcharged.
• Risks: As with CP charging, there’s a risk of exceeding safe current or voltage limits if the transition between power-based charging and voltage-based charging isn’t well managed.

Part 2. 7 Types of lithium battery discharging methods: CC, CV, CC-CV, CP, CP-CC-CV, CR, CR-CV

In addition to the CC discharge method required by the standard, lithium batteries can also be discharged by CV, CC-CV, CP, CP-CC-CV, CR, CR-CV, etc.

1. Constant Current (CC) Discharging

Figure 6: Constant Current Discharge Curve

Constant Current (CC) discharging involves discharging the battery at a fixed current, regardless of the voltage drop as the battery discharges.

• How it works: During CC discharging, the battery’s current output remains constant. As the battery discharges, the voltage gradually decreases. This method is typically used in applications where a consistent current is required from the battery, and the device is designed to handle the drop in voltage.
• Why it’s used: CC discharging is useful in systems where stable current is critical, such as power supplies, testing devices, or energy storage systems that need consistent performance.
• Risks: If the battery discharges too deeply, it may lead to over-discharge, which can damage the battery and reduce its lifespan.

2. Constant Voltage (CV) Discharging

Figure 7: Constant Voltage Discharge Curve    

Constant Voltage (CV) discharging is a method where the battery voltage is held constant while the current decreases as the battery discharges.

• How it works: In this method, the voltage remains steady while the current gradually drops. This approach is typically used when maintaining a stable voltage output is more important than the rate at which the battery discharges.
• Why it’s used: CV discharging is used in applications where the device or circuit requires a consistent voltage for a period of time, regardless of the battery’s state of charge.
• Risks: If not carefully managed, holding the voltage constant could lead to the battery being excessively drained, which may damage the cells or reduce capacity over time.

3. CC-CV (Constant Current – Constant Voltage) Discharging

Figure 8: Constant current and constant voltage discharge curve

CC-CV discharging combines constant current and constant voltage phases. Initially, the battery discharges at a constant current until the voltage reaches a pre-defined threshold, after which the voltage is held constant, and the current decreases.

How it works:

• CC phase: The battery discharges at a fixed current, and its voltage gradually drops.
• CV phase: Once the voltage limit is reached, the current starts to decrease, and the voltage is maintained at a steady value.
• Why it’s used: CC-CV discharging is commonly used in systems that require a stable output voltage or where the device can handle both constant current and constant voltage stages. It helps prevent deep discharge and maintains performance during the discharge cycle.
• Risks: If the transition from CC to CV is not done properly, there could be issues with over-discharge or inefficiency.

4. Constant Power (CP) Discharging

Figure 9: Constant power discharge curve

Constant Power (CP) discharging is a method where the power output (measured in watts) is kept constant while the current and voltage adjust dynamically to meet the power demand.

• How it works: During CP discharging, the battery maintains a constant power level, meaning that the current and voltage are adjusted as needed to keep the power output steady. This method is typically used in applications where a constant power consumption is critical, such as in certain energy storage systems or power electronics.
• Why it’s used: CP discharging is ideal for scenarios where power output is the primary concern, and the system needs to maintain consistent energy delivery, despite variations in battery voltage.
• Risks: Since the current and voltage can fluctuate, it may lead to less efficient discharge or cause issues with voltage limits, potentially resulting in over-discharge or excessive battery strain.

5. CP-CC-CV (Constant Power – Constant Current – Constant Voltage) Discharging

Figure 10: Constant power constant current constant voltage discharge curve

CP-CC-CV discharging is a more advanced and hybrid approach that integrates constant power, constant current, and constant voltage phases during the discharge cycle.

• CP phase: The battery discharges at a fixed power output, with the current and voltage dynamically adjusting.
• CC phase: As the battery voltage drops, the current is maintained constant for a period.
• CV phase: Once the voltage limit is reached, the voltage is held constant, and the current decreases.
• Why it’s used: This method is particularly useful in systems where power needs to be delivered at a stable rate throughout the discharge process, while ensuring the battery voltage and current stay within safe limits as it approaches depletion.
• Risks: The complexity of managing three phases can make this method more difficult to implement, and improper transitions between phases can lead to over-discharge or inefficiency.

6. Constant Resistance (CR) Discharging

Figure 11: Constant resistance discharge curve

Constant Resistance (CR) discharging involves discharging the battery through a fixed resistance. The current varies depending on the battery voltage, but the load resistance remains constant throughout the discharge.

• How it works: The battery is connected to a resistor with a fixed resistance value. As the battery discharges, the voltage decreases, causing the current to drop according to Ohm’s law (I = V/R). The resistance is kept constant, but the current will decrease as the voltage decreases.
• Why it’s used: CR discharging is often used for testing the battery’s behavior under different load conditions. It helps simulate real-world usage scenarios where devices operate at a fixed resistance, like some sensors or small electronic gadgets.
• Risks: The primary concern with CR discharging is that the battery can discharge too quickly if the load is too low, leading to potential over-discharge. Additionally, managing constant resistance for certain applications might not be efficient enough for optimal battery performance.

7. CR-CV (Constant Resistance – Constant Voltage) Discharging

Figure 12: Constant resistance and constant voltage discharge curve

CR-CV discharging combines constant resistance with a constant voltage phase. Initially, the battery discharges through a fixed resistance, but once the voltage reaches a certain point, the voltage is held constant, and the current decreases.

• CR phase: The battery discharges through a constant resistance, and as the voltage decreases, the current also drops.
• CV phase: Once the voltage reaches a pre-defined threshold, the charging system switches to constant voltage mode, where the voltage is kept steady, and the current decreases.
• Why it’s used: This method is used when both the load conditions (constant resistance) and battery protection (constant voltage) need to be managed together. It is especially useful in battery testing and some low-power applications.
• Risks: Similar to other discharging methods, improper transition from CR to CV phases could lead to over-discharge, especially if the resistance is too low or the battery is not designed to handle it.

Part 3. The most common charging method of lithium batteries

In summary, the charging and discharging methods of lithium batteries are diverse, but in the final analysis, they are single-step or combined processes based on CC (constant current), CV (constant voltage), CP (constant power) or CR (constant resistance). The current and voltage changes of these charging and discharging methods are shown in the table below.

Comparison of current and voltage changes in different charging and discharging methods table

At present, the mainstream charging method of lithium batteries is still mainly CC-CV.

This is because lithium batteries have polarization phenomenon (that is, the instant voltage is not a steady-state voltage). In the CC stage, the current is large and the charging speed is fast. After the voltage rises to the upper limit voltage, it maintains a constant potential. The electrons in the external circuit react with Li+ at the negative electrode.

As the negative electrode inserts lithium, the active sites decrease, the number of electrons participating in the reaction decreases, and the current gradually decreases. When the current is reduced to 0 (ideal situation), the polarization is completely eliminated and the lithium battery is fully charged.

However, during the discharge process, lithium batteries usually use CC mode, which may be to make it easier to calculate capacity or estimate SOC. In actual working conditions, constant power discharge is mostly used.

Part 4. How to choose the charging and discharging method of lithium batteries?

The selection of lithium battery charging and discharging methods should take into account the convenience of data processing, charging/discharging efficiency, and the risk of internal damage to lithium batteries. It is necessary to give full play to the performance of lithium batteries and to conduct fast and accurate detection.

At present, lithium batteries are mainly tested in CC-CV charging mode and CC discharge mode, but in actual terminal use conditions, CP mode is the main mode.

Part 5. FAQs

What is the difference between CC and CV charging methods?

The main difference between CC and CV charging methods lies in how the current and voltage are managed: In CC mode, the charging current is kept constant, and the voltage rises. In CV mode, once the voltage limit is reached, the current is reduced, and the voltage stays constant. The two methods work together in the CC-CV charging process, which ensures efficient and safe charging of lithium batteries.

How does CC-CV charging protect the lithium-ion battery from overcharging?

The CC-CV charging process protects lithium-ion batteries from overcharging by first applying a constant current until the battery reaches its maximum voltage (typically 4.2V). Once this voltage limit is reached, the charger switches to constant voltage mode, reducing the charging current. This prevents the battery from receiving excessive current, which could otherwise cause overheating, battery swelling, or even thermal runaway.

What happens if you use constant current charging for too long?

If constant current charging is used for too long without switching to constant voltage, the battery could be overcharged, which can damage the battery cells. This can result in overheating, capacity loss, and even dangerous conditions like battery swelling or thermal runaway. That’s why the transition to constant voltage (CV) is essential in ensuring the battery is safely charged and protected from damage.

When should you use CP or CP-CV charging methods for lithium batteries?

CP and CP-CV charging methods are typically used in specific applications where power rather than current or voltage needs to be carefully regulated. For example, CP charging might be used in high-power applications like electric vehicles or renewable energy storage systems where a consistent power output is necessary to optimize battery efficiency. CP-CV charging would then take over once the battery approaches full charge to ensure voltage does not exceed the battery’s safe limit.

Can a lithium battery be damaged by using the wrong charging method?

Yes, using the wrong charging method can damage a lithium battery. For instance, using constant current (CC) without transitioning to constant voltage (CV) can overcharge the battery, potentially causing overheating or thermal runaway. Similarly, using constant power (CP) charging without proper regulation can lead to excessive current or voltage being applied, which may degrade the battery’s lifespan or cause it to fail prematurely. Always follow the manufacturer’s recommended charging method for optimal performance and safety.