Battery Voltage Explained: Nominal, Charged, Minimum, and Cut-Off Levels

by Mike Beard in Battery Knowledge Base

When selecting a lithium-ion battery pack, understanding its voltage characteristics is crucial for ensuring optimal performance and longevity. Three key voltage terms define a battery's operation: Nominal Voltage, Charged Voltage, and Cut-Off Voltage. Each of these plays a role in how the battery functions and determines its compatibility with different applications.

1. Nominal Voltage: The Standard Operating Voltage

What Is Nominal Voltage?

Nominal voltage is roughly the average voltage at which a battery operates under normal conditions. It represents a balance between the battery being fully charged and fully discharged. This value is commonly used to specify battery packs and serves as a general reference for comparing different battery chemistries.

Example Nominal Voltages for Different Lithium Batteries:

  • Lithium-Ion (Li-ion): 3.6V per cell

  • Lithium-Polymer (LiPo): 3.7V per cell

  • Lithium Iron Phosphate (LiFePO4): 3.2V per cell

For a 3S Li-ion battery pack (three cells in series), the nominal voltage would be 10.8V (3.6V × 3).

2. Charged Voltage: The Maximum Voltage When Fully Charged

What Is Charged Voltage?

Charged voltage (also called full-charge voltage) is the highest voltage a cell reaches when fully charged. Exceeding this voltage can damage the battery and reduce its lifespan, so proper charging is crucial.

Example Charged Voltages for Lithium Batteries:

  • Lithium-Ion (Li-ion): 4.2V per cell

  • Lithium-Polymer (LiPo): 4.2V per cell

  • Lithium Iron Phosphate (LiFePO4): 3.65V per cell

For a 3S Li-ion battery pack, the fully charged voltage would be 12.6V (4.2V × 3).

Why Does Charged Voltage Matter?

  • Ensures the battery delivers maximum energy capacity.

  • Helps determine charging cutoff limits for battery chargers.

  • Overcharging can cause overheating, swelling, and reduced battery life.

3. Minimum Voltage: The Absolute Lowest Safe Voltage

What Is Minimum Voltage?

Minimum voltage is the absolute lowest voltage a battery cell can reach before severe degradation or damage occurs. While batteries should generally not be discharged this low, it serves as a hard limit for extreme conditions.

Example Minimum Voltages for Lithium Batteries:

  • Lithium-Ion (Li-ion): 2.5V per cell

  • Lithium-Polymer (LiPo): 2.8V per cell

  • Lithium Iron Phosphate (LiFePO4): 2.0V per cell

For a 3S Li-ion battery pack, the absolute minimum voltage would be 7.5V (2.5V × 3).

Why Is Minimum Voltage Important?

  • Going below this voltage can cause irreversible damage to battery cells.

  • If a battery drops below its minimum voltage, it may become unchargeable.

  • Battery management systems (BMS) typically prevent discharge beyond this level.

4. Cut-Off Voltage: The Recommended Safe Discharge Limit

What Is Cut-Off Voltage?

Cut-off voltage is the recommended minimum voltage where a battery should stop discharging to prevent long-term damage. It is usually about 0.2V higher per cell than the absolute minimum voltage.

Example Cut-Off Voltages for Lithium Batteries:

  • Lithium-Ion (Li-ion): 2.7V per cell

  • Lithium-Polymer (LiPo): 3.0V per cell

  • Lithium Iron Phosphate (LiFePO4): 2.2V per cell

For a 3S Li-ion battery pack, the recommended cut-off voltage would be 8.1V (2.7V × 3).

Why Is Cut-Off Voltage Important?

  • Helps prevent deep discharge, which reduces battery lifespan.

  • Ensures stable performance and long-term usability.

  • Used by battery management systems (BMS) to regulate power usage.

Comparing Nominal, Charged, Minimum, and Cut-Off Voltages

Battery Type Nominal Voltage Charged Voltage Cut-Off Voltage Minimum Voltage
Li-ion 3.6V 4.2V 2.7V 2.5V
LiPo 3.7V 4.2V 3.5V 3.0V
LiFePO4 3.2V 3.65V 2.7V 2.5V

What Is Cut-Off Voltage?

Cut-off voltage is the lowest voltage a battery cell should reach before it is considered discharged. Discharging below this level can lead to permanent damage, capacity loss, and battery failure.

Example Cut-Off Voltages for Lithium Batteries:

  • Lithium-Ion (Li-ion): 2.5V - 2.8V per cell

  • Lithium-Polymer (LiPo): 3.5V per cell

  • Lithium Iron Phosphate (LiFePO4): 2.7V per cell

For a 3S Li-ion battery pack, the cut-off voltage would be 7.5V (2.5V × 3).

Why Is Cut-Off Voltage Important?

  • Prevents deep discharge, which can permanently damage the battery.

  • Ensures longer cycle life and stable performance.

  • Battery management systems (BMS) monitor and prevent discharging beyond this level.

Conclusion

Understanding nominal, charged, and cut-off voltages is essential when choosing a battery pack for your application. Nominal voltage defines the battery’s general operating range, charged voltage determines its full power capacity, and cut-off voltage ensures safe discharge limits. Ensuring your battery operates within these voltage limits will maximize its lifespan and maintain safe performance. If you're unsure which battery pack best fits your needs, our team is here to help!

 

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