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What is the best float voltage for LiFePO4?

What is the best float voltage for LiFePO4?
The best float voltage for LiFePO4 batteries is typically between 13.2 and 13.8 V. This voltage range ensures the battery remains in a stable state when fully charged and not in use. It is recommended to maintain the float voltage within this range to prevent overcharging or discharging. The 12V Battle Born Batteries are designed to operate comfortably within this optimal float voltage range.
  1. Optimal Float Voltage Range:
    The recommended float voltage range for LiFePO4 batteries is between 13.2 and 13.8 V. This range allows the battery to maintain a stable charge without the risk of overcharging or discharging. It is important to keep the float voltage within this range to ensure the longevity and performance of the LiFePO4 battery.
  2. Stability and Battery Health:
    By maintaining the float voltage within the optimal range, you can prevent overcharging, which can lead to excessive heat generation and reduced battery lifespan. Similarly, avoiding a float voltage below the recommended range helps prevent discharging, which can result in a loss of battery capacity and performance.
  3. Battle Born Batteries:
    The 12V Battle Born Batteries are specifically designed to operate comfortably within the optimal float voltage range of 13.2 to 13.8 V. These batteries are engineered to provide reliable and long-lasting performance while maintaining a stable charge level. By choosing batteries that are designed for the recommended float voltage range, you can ensure optimal performance and maximize the lifespan of your LiFePO4 battery.

LiFePO4 Cell voltage chart. What is the best float voltage for LiFePO4?

Charging Mastervolt Gel and AGM Batteries

Charge Voltage and Phases

Mastervolt gel and AGM batteries, whether 2 V, 6 V, or 12 V, require specific voltage settings to charge effectively. For 12 V systems, the charging voltage is set at 14.25 V, and for 24 V systems, it is 28.5 V. The charging process is divided into distinct phases:

  1. Absorption Phase: Maintains the voltage at 14.25 V (12 V systems) or 28.5 V (24 V systems) until the battery reaches full charge.
  2. Float Phase: Reduces the voltage to 13.8 V for 12 V systems and 27.6 V for 24 V systems to maintain the battery’s charge without overcharging.

These figures are based on a standard temperature of 25°C.

Wet Lead-Acid Batteries

Similar to gel and AGM batteries, wet lead-acid batteries also require an absorption voltage of 14.25 V for 12 V systems and 28.5 V for 24 V systems. However, the float voltage differs slightly at 13.25 V for 12 V and 26.5 V for 24 V systems.

Charging Mastervolt Lithium Ion Batteries

Charge Voltage and Phases

Lithium Ion batteries follow a similar absorption voltage of 14.25 V for 12 V systems and 28.5 V for 24 V systems. The float voltage is slightly lower than that for gel and AGM batteries, set at 13.5 V for 12 V systems and 27 V for 24 V systems. Notably, temperature adjustments are not required for Lithium Ion batteries, simplifying their management.

Charge Current Recommendations

Gel and AGM Batteries

The recommended charging current for gel and AGM batteries should be between 15% to 25% of the battery’s capacity. For instance, a 400 Ah battery would need a charger that can provide between 60 and 100 amperes, considering additional load requirements.

  • Maximum Charge Current:
    • Gel batteries: 50% of capacity.
    • AGM batteries: 30% of capacity.

Lithium Ion Batteries

Lithium Ion batteries can tolerate higher charging currents, but to extend their lifespan, it is recommended to limit the charge current to 30% of the battery capacity. For example, a 180 Ah Lithium Ion battery should ideally be charged at 60 amperes.

Temperature Compensation for Optimal Protection

Modern Mastervolt battery chargers utilize a three-step+ charging characteristic, continuously regulating charge voltage and current. For gel and AGM batteries, using a temperature sensor to adjust the charging voltage based on the battery’s temperature can significantly prolong battery life. This is known as ‘temperature compensation’.

Temperature Compensation Curve

To protect the connected devices and the battery itself, temperature compensation adjusts the voltage:

  • Maximum offsetting effect: 14.55 V for 12 V systems and 29.1 V for 24 V systems.

At extreme temperatures, gel and AGM batteries may not charge properly, but connected devices will still be powered.

Calculating Charging Time

Efficiency Considerations

Battery efficiency impacts charging time:

  • Wet batteries: Approximately 80% efficient.
  • Gel and AGM batteries: 85% to 90% efficient.
  • Lithium Ion batteries: Up to 97% efficient.

Charging Time Formula

For Gel or AGM batteries: Lt=Coeff×(Al−Ab)

For Lithium Ion batteries, adjust the efficiency value as appropriate.

Ripple Voltage Impact

Ripple voltage from chargers can cause premature battery failure and equipment malfunction. Mastervolt chargers ensure ripple voltage stays below 100 mV, minimizing risk.

State of Charge Measurement

Accurately measuring the state of charge is essential for proper battery management. Using an amp hour meter, such as the Mastervolt MasterShunt, provides precise data on battery voltage, charge/discharge currents, and historical data for better management decisions.

Peukert’s Law and Battery Discharge

Peukert’s Law helps calculate the actual battery capacity under varying discharge rates, which is crucial for accurately determining how long a battery can supply power. This law, however, does not apply to Lithium Ion batteries.

Peukert’s Formula



  • Cp = Battery capacity at a given discharge current
  • I = Discharge current level
  • n = Peukert exponent

Ventilation Requirements

Adequate ventilation is necessary to dissipate the heat generated during battery charging. For instance, a 12 V/400 Ah battery set with an 80-amp charger requires 6 m³/h of ventilation.

Ventilation Formula



  • Q = Required ventilation in m³/h
  • I = Maximum charge current
  • f1, f2 = Reduction factors for battery type
  • n = Number of cells


By following these detailed guidelines for charging Mastervolt batteries, you can ensure optimal performance and longevity for your battery systems. Proper voltage settings, current management, temperature compensation, and ventilation are crucial factors in maintaining the health and efficiency of your batteries.

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