Battery Equivalents and Replacements

LiFePO4 Battery Voltage Chart

Lithium Iron Phosphate (LiFePO4) batteries have gained prominence in various applications, including renewable energy storage, electric vehicles, and backup power systems.

Understanding the voltage characteristics of these batteries is essential for optimizing performance, maintaining longevity, and ensuring safe operation.

Published: May 4, 2024.

lifepo4 battery

Understanding the Voltage-SOC Relationship

The relationship between voltage and state of charge (SOC) is fundamental to managing and optimizing LiFePO4 (Lithium Iron Phosphate) batteries.

Open Circuit Voltage (OCV)

The Open Circuit Voltage (OCV) is a key parameter for LiFePO4 batteries, representing the battery's voltage when it is not under load or in use. OCV offers a direct indication of the battery's SOC, serving as a valuable tool for monitoring and management.

For instance, a fully charged 12V LiFePO4 battery typically exhibits an OCV of around 13.6V.

Conversely, when fully discharged, the OCV can drop to around 10V. Understanding these voltage ranges helps users ascertain the battery's charge level and prevents unexpected power loss.

SOC Voltage Ranges

Mapping voltage to specific SOC percentages is crucial for accurate monitoring and management. A LiFePO4 battery's voltage changes in a non-linear fashion as it discharges, which can be categorized into the following ranges:

  • 100% SOC: At full charge, the OCV is typically around 13.6V (fully charged battery at rest) and 14.6V (fully charged battery still charging) for a 12V LiFePO4 battery, though this can vary slightly depending on the battery's design and specifications.
  • 80-90% SOC: The voltage decreases gradually, reaching around 13.3V to 13.4V, indicating a partially charged battery.
  • 50% SOC: As the battery discharges further, the voltage stabilizes around 13V, indicating a half-charged state. This plateau is unique to LiFePO4 batteries, providing steady voltage despite further discharge.
  • 20-30% SOC: At this level, the voltage drops more noticeably, ranging around 12.8V and 12.9V, signaling the need for recharging soon.
  • 0-10% SOC: A fully discharged battery's voltage can drop to around 10V, marking the end of its usable capacity.

Understanding these voltage ranges helps users gauge the battery's remaining charge and make informed decisions about recharging or reducing load to extend its lifespan.

Voltage Plateau

One of the unique characteristics of LiFePO4 batteries is the relatively stable voltage plateau during discharge. After an initial drop from a full charge, the voltage levels off, maintaining a consistent range for a significant portion of the discharge cycle. This plateau typically sits around 13V (12.8V - 13.3V) for a 12V LiFePO4 battery, providing steady power output.

This stable voltage is beneficial for applications requiring consistent power, such as electric vehicles and solar energy storage systems. It also makes SOC estimation based on voltage alone more challenging, emphasizing the importance of using additional metrics, such as coulomb counting, to accurately gauge the battery's charge.

LiFePO4 3.2V, 12V, 24V, 36V, and 48V Battery Voltage Chart

The following LiFePO4 battery voltage chart lists the voltages of 3.2V (since cell), 12V (four cells), 24V (eight cells), 36V (twelve cells), and (sixteen cells) 48V LiFePO4 batteries depending on the SOC level.

State of Charge (SoC)
3.2V 12V 24V 36V 48V
100% Charging 3.65V 14.6V 29.2V 43.8V 58.4V
100% Rest 3.40V 13.6V 27.2V 40.8V 54.4V
90% 3.35V 13.4V 26.8V 40.2V 53.6V
80% 3.32V 13.3V 26.6V 39.9V 53.1V
70% 3.30V 13.2V 26.4V 39.6V 52.8V
60% 3.27V 13.1V 26.2V 39.3V 52.3V
50% 3.26V 13.0V 26.0V 39.1V 52.1V
40% 3.25V 13.0V 26.0V 39.0V 52.0V
30% 3.22V 12.9V 25.8V 38.6V 51.5V
20% 3.20V 12.8V 25.6V 38.4V 51.2V
10% 3.00V 12.0V 24.0V 36.0V 48.0V
0% 2.50V 10.0V 20.0V 30.0V 40.0V

Note: some differences between exact battery chemistries, types, and models are possible. Thus, whenever possible, check the charts that came with your specific battery.

Safe Charging and Discharging Practices

Proper charging and discharging practices are critical for maintaining the integrity, performance, and lifespan of LiFePO4 batteries.

Charging Voltage Limits

LiFePO4 batteries are designed to operate within specific voltage ranges, particularly during charging. For a 12V LiFePO4 battery, the maximum recommended charging voltage is typically 14.4V to 14.6V. Charging above this voltage risks overcharging the battery, which can degrade its capacity over time and potentially damage its internal structure.

To avoid overcharging, it's essential to use a charger specifically designed for LiFePO4 batteries or one with adjustable settings that can be configured to these specific limits. Additionally, many LiFePO4 batteries include a Battery Management System (BMS) that prevents charging beyond safe limits, ensuring the battery’s longevity and safety.

Charging Profiles

LiFePO4 batteries benefit from a specific charging profile known as Constant Current/Constant Voltage (CC/CV). This charging method consists of two main phases:

  • Constant Current (CC): In this phase, the charger supplies a steady current to the battery until it reaches its maximum voltage limit. This phase ensures the battery charges efficiently without overheating or causing internal damage.
  • Constant Voltage (CV): Once the battery reaches its maximum voltage limit (typically 14.4V to 14.6V for a 12V battery), the charger transitions to the CV phase. During this phase, the charger maintains a constant voltage, gradually reducing the charging current until it approaches zero. This ensures the battery reaches full capacity without overcharging, further extending its life.

Discharge Voltage Ranges

Proper discharging practices are equally important for maintaining the health of LiFePO4 batteries. For a 12V LiFePO4 battery, it's crucial to avoid discharging below 10V. Doing so risks over-discharging, which can significantly degrade the battery's capacity and reduce its lifespan.

Many LiFePO4 batteries are equipped with a BMS that protects against over-discharging by cutting off the battery's output once it reaches a safe minimum voltage.

For batteries without a BMS, it’s essential to monitor the voltage regularly or use an external device designed to prevent over-discharging, safeguarding the battery’s longevity.

LiFePO4 Battery Charging/Discharging Voltages

The following chart lists typical voltage ranges for 12V (four cells), 24V (eight cells), 36V (twelve cells), and 48V (sixteen cells) LiFePO4 batteries:

LiFePO4 Battery Voltages 12V 24V 36V 48V
Charging Voltage 14.2-14.6V 28.4V-29.2V 42.6V-43.8V 56.8V-58.4V
Float Voltage 13.6V 27.2V 40.8V 54.4V
Maximum Voltage 14.6V 29.2V 43.8V 58.4V
Nominal Voltage 12V (12.8V) 24V (25.6V) 36V (38.4V) 48V (51.2V)
Minimum (Cutoff) Voltage 10V 20V 30V 40V

Note: again, some differences between these values are possible, considering all the models and types of LiFePO4 batteries on the market today.

How to Check LiFePO4 Battery Remaining Capacity?

Monitoring the remaining capacity of a LiFePO4 battery is very important for ensuring reliable performance and preventing over-discharging. This process can be challenging due to the unique discharge characteristics of LiFePO4 batteries.

Voltage Monitoring

One straightforward method for estimating a LiFePO4 battery's remaining capacity is to monitor its voltage. The relationship between voltage and state of charge (SOC) offers a rough indication of the remaining capacity:

  • OCV to SOC Mapping: Open Circuit Voltage (OCV) gives a direct snapshot of the battery's SOC when not under load. For example, a 12V LiFePO4 battery typically shows an OCV of around 13.6V/14.6V at full charge (resting/charging) and around 10V when fully discharged.
  • Voltage Plateau: LiFePO4 batteries exhibit a stable voltage plateau around 13V for a significant portion of their discharge cycle, making it difficult to estimate remaining capacity based on voltage alone during this stage.
  • Voltage Drop: Once the battery drops below its plateau, a more significant voltage drop indicates it is nearing its lower capacity limit, signaling the need to recharge.

Coulomb Counting

A more accurate way to gauge a LiFePO4 battery's remaining capacity is through coulomb counting, which involves measuring the amount of energy flowing in and out of the battery:

  • Current Monitoring: This technique relies on a meter or Battery Management System (BMS) to track the current going in and out during charging and discharging cycles. By integrating this current over time, it calculates the total charge entering or leaving the battery, providing an accurate estimate of its remaining capacity.
  • Digital Battery Monitors: Advanced battery monitors can provide real-time SOC estimates by combining voltage monitoring and coulomb counting, making them an ideal solution for more accurate capacity management.

Battery Management Systems (BMS)

LiFePO4 batteries often come equipped with a built-in BMS that helps manage the battery's charge and discharge cycles, preventing overcharging and over-discharging:

  • SOC Indicator: Many BMS systems include a digital display or indicator that provides information about the battery's remaining capacity, simplifying monitoring.
  • Balancing: BMS systems also balance the charge across individual cells, preventing voltage imbalances that can lead to inaccurate capacity readings or potential damage.

Monitoring a LiFePO4 battery's remaining capacity is crucial for ensuring reliable performance and preventing over-discharging.

Voltage monitoring provides a rough estimate of SOC, while coulomb counting and digital battery monitors offer more accurate assessments.

Also, a built-in BMS enhances capacity management, balancing the charge across cells and preventing imbalances.

LiFePO4 Battery Voltage/Discharge Current Dependency

LiFePO4 batteries are known for their consistent performance and stable voltage characteristics.

However, the relationship between output voltage and discharge current can vary depending on the battery's state of charge (SoC) and load.

Impact of Discharge Current on Voltage

Discharge current significantly influences a LiFePO4 battery's voltage, particularly at varying levels of SoC:

  • High Discharge Current: When the battery is under a high discharge current, such as during heavy loads or demanding applications, the internal resistance causes a voltage drop. This internal resistance manifests as a decrease in the output voltage proportional to the current drawn, affecting the battery's performance.
  • Low Discharge Current: In contrast, low discharge currents result in minimal voltage drop, allowing the battery to maintain its voltage plateau for longer. This steady state ensures consistent power output, crucial for applications requiring reliable energy delivery.
  • Voltage Recovery: Once the load is removed or reduced, the voltage may recover slightly, reflecting the battery's true SoC more accurately.

Internal Resistance and Temperature Effects

Internal resistance and temperature play key roles in determining how the discharge current affects a LiFePO4 battery's voltage:

  • Internal Resistance: The internal resistance contributes to voltage drop under load, increasing as the battery's SoC decreases or its temperature fluctuates.
  • Temperature: Higher temperatures generally reduce internal resistance, mitigating voltage drop during discharge, while lower temperatures increase resistance, amplifying the voltage drop.

LiFePO4 battery voltage is inherently linked to both its SoC and discharge current.

High discharge currents cause voltage drops due to internal resistance, while low currents allow the battery to maintain its voltage plateau for longer.

Internal resistance and temperature also influence this relationship, affecting how discharge currents impact output voltage.

However, all these values are highly individual for each battery and depend on the battery capacity, construction, type, model, brand, etc.

Benefits of LiFePO4 Batteries

LiFePO4 batteries have gained significant traction across various industries due to their unique advantages.

Thermal Stability

One of the most notable benefits of LiFePO4 batteries is their superior thermal stability.

Unlike other lithium-ion chemistries, LiFePO4 batteries are more resistant to thermal runaway, a dangerous condition where the battery's temperature escalates uncontrollably, potentially leading to fire or explosion. This stability is attributed to the robust chemical structure of LiFePO4, which makes it inherently safer and more stable under various operating conditions.

This thermal stability allows LiFePO4 batteries to be used in a broader range of applications, including high-temperature environments and settings requiring extensive charging and discharging cycles, without risking safety or reliability.

Longevity

LiFePO4 batteries are renowned for their extended cycle life, offering up to 2000 to 5000 charge-discharge cycles, depending on the specific model and operating conditions.

This longevity significantly surpasses other lithium-ion chemistries, making LiFePO4 batteries a more cost-effective option over time.

The long lifespan is particularly advantageous for applications such as solar energy storage, where batteries need to endure frequent charge and discharge cycles.

Additionally, the stable voltage plateau throughout discharge cycles contributes to the battery's longevity, preventing drastic drops in capacity over time and ensuring consistent performance.

Performance Consistency

LiFePO4 batteries offer consistent performance, characterized by a stable voltage plateau during discharge. This feature ensures steady power output for a significant portion of the battery's discharge cycle, making it ideal for applications requiring reliable energy delivery, such as electric vehicles and off-grid solar systems.

This performance consistency also simplifies power management, as users can rely on predictable voltage levels to gauge remaining capacity.

Additionally, LiFePO4 batteries exhibit lower self-discharge rates compared to other lithium-ion chemistries, preserving their charge for longer periods when not in use, further enhancing their reliability.

Environmental Friendliness

LiFePO4 batteries are also considered more environmentally friendly than other lithium-ion chemistries.

They do not contain toxic metals such as cobalt or nickel, reducing their environmental impact both during production and disposal.

Also, the longer lifespan of LiFePO4 batteries contributes to reduced waste, making them a more sustainable choice for various applications.

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The benefits of LiFePO4 batteries make them a versatile and reliable choice for numerous applications.

Their thermal stability ensures safe operation in diverse environments, while their extended lifespan and consistent performance make them suitable for long-term, high-demand uses.

Additionally, their environmentally friendly design reduces their impact on the planet, making LiFePO4 batteries an ideal choice for applications ranging from electric vehicles to renewable energy storage.