Why Battery Management Systems are Important in Lithium Iron Phosphate Batteries

Posted November 27, 2018


Lithium iron phosphate batteries pack a lot of power and value into a small package. The chemistry of these batteries is a big part of their superior performance. But all reputable commercial lithium-ion batteries also include another important element along with the battery cells themselves: a carefully designed electronic battery management system (BMS). A well-designed battery management system protects, and monitors a lithium-ion battery to optimize performance, maximize lifetime, and ensure safe operation over a wide range of conditions.

At RELiON, all our lithium iron phosphate batteries include an internal or external BMS. Let’s have a look at how a RELiON BMS protects and optimizes the operation of a lithium iron phosphate battery.

1. Over and Under Voltage

Lithium iron phosphate cells operate safely over a range of voltages, typically from 2.0V to 4.2V. Some lithium chemistries result in cells that are highly sensitive to overvoltage, but LiFePO4 cells are more tolerant. Still, significant overvoltage for a prolonged period during charging can cause plating of metallic lithium on the battery’s anode which permanently degrades performance. Also, the cathode material may oxidize, become less stable, and produce carbon dioxide which may lead to a buildup of pressure in the cell. All RELiON battery management systems limit each cell and the battery itself to a maximum voltage. The BMS in the RELiON RB100 LiFePO4 battery, for example, protects each cell in the battery and limits the voltage in the battery to 15.6V.

Undervoltage during battery discharge is also a concern since discharging a LiFePO4 cell below approximately 2.0V may result in a breakdown of the electrode materials. Lithium batteries have a recommended minimum operational voltage. In the RELiON RB100, for example, the minimum recommended voltage is 11V. The BMS acts as a failsafe to disconnect the battery from the circuit if any cell drops below 2.0V.

2. Overcurrent and Short Circuit Protection

Every battery has a maximum specified current for safe operation. If a load is applied to the battery which draws a higher current, it can result in overheating the battery. While it’s important to use the battery in a way to keep the current draw below the maximum specification, the BMS again acts as a backstop against overcurrent conditions and disconnects the battery from operation.

Again, using the RB100 as an example, the maximum continuous discharge current is specified at 100A, the peak discharge current is 200A, and the BMS disconnects the battery from the circuit if the load draws about 280A.

A short circuit of the battery is the most serious form of overcurrent condition. It most commonly happens when the electrodes are accidentally connected with a piece of metal. The BMS must quickly detect a short circuit condition before the sudden and massive current draw overheats the battery and causes catastrophic damage. In the RB100, the battery shuts down within 200-600 microseconds of an external short circuit, then resumes normal operation if the short circuit condition is removed.

3. Over Temperature

Unlike lead-acid or lithium cobalt oxide batteries, lithium iron phosphate batteries operate efficiently and safely at temperatures up to 60oC or more. But at higher operating and storage temperatures, as with all batteries, the electrode materials will begin to degrade. The BMS of a lithium battery uses embedded thermistors to actively monitor the temperature during operation, and it will disconnect the battery from the circuit at a specified temperature. In the example of the RELiON RB100, the BMS disconnects the battery at 80oC (176oF) and reconnects the battery at 50oC (122oF).

4. Cell Imbalance

Lithium-ion batteries have a major difference from lead-acid batteries when it comes to balancing the voltage in each individual cell during charging. Because of small differences in manufacturing or operating conditions, each cell in a battery charges at a slightly different rate. In a lead-acid battery, if one cell charges faster and reaches its full voltage, the typical low end of charge current, along with the excess charge-return, will ensure the other cells get fully charged. In a sense, the cells in a lead-acid battery are self-equalizing during charge.

This is not the case with lithium-ion batteries. When a lithium-ion cell is fully charged, its voltage begins to rise further which may lead to electrode damage. If the charge of the entire battery is stopped when only one cell is fully charged, the remaining cells do not reach full charge and the battery will operate below peak capacity. A well-designed BMS will ensure each cell safely and fully charges before the entire charging process is complete.


Lithium iron phosphate batteries are made up of more than just individual cells connected together. They also include a battery management system (BMS) which, while not usually visible to the end user, makes sure each cell in the battery remains within safe limits. All RELiON lithium iron phosphate batteries include an internal or external BMS to protect, control, and monitor the battery to ensure safety and maximum lifetime over the full range of operating conditions.



  • Thomas Leshick

    I'm interested in the cold weather charges. I live in N.Y. and it gets colder than what is recommended charge temperatures. We traveled in the spring and the temperature was 26 f. Well below freezing.

  • Daniel Walker

    Thank You for sharing this information with us. All the information that you shared with us is very valuable and important for those who don't know about Batteries and for those as well who are doing business related this. I am also one of them. This information is also very useful for me as well. Just Check out at:- https://batteryspecialists.com.au/

  • Eric Schmitt

    Also interested in a LiFePO4 system for a 4 season climate and that last comment wasn't helpful.

  • Puuja

    Nice article, Lithium ion battery market has great scope, The overall lithium ion battery market is expected to grow from USD 37.4 billion in 2018 to USD 92.2 billion by 2024, at a CAGR of 16.2%.
    Source: https://www.marketsandmarkets.com/Market-Reports/lithium-ion-battery-market-49714593.html

  • Reiner Teo

    Please advise what will happen to the LiFePO4 battery if the BMS within the battery is faulty. How will the battery operate with faulty BMS.

  • RELiON

    Reiner - A faulty BMS typically fails in an Open state not allowing the battery to operate at all. There will be no voltage or current available at the battery terminals, until the faulty BMS is removed, repaired and/or replaced.

  • Iron Edison

    Lithium ion battery cells have two critical design issues; if you overcharge them you can damage them and cause overheating and even explosion or flame so it's important to have a battery management system to provide overvoltage protection .

    Lithium ion cells can also be damaged if they're discharged below a certain threshold, approximately 5 percent of total capacity. If the cells are discharged below this threshold their capacity can become permanently reduced.

  • MD Rahmat Ali

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  • Rohit Singh

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  • Battery Boy

    I'm having trouble charging my new-to-me RB100 100ah lithium iron battery. I've tried 2 battery chargers and a MMPT controller. I'm getting a 9+ volt reading on a multimeter on open terminals. When I attach anything to the terminals (charger, controller) the voltage drops to ~2-3 volts. Do I need to "boost" the voltage up so that other device can "see" it? I won't do anything until I talk to Relion tech support, but could use some info in the meantime.

  • RELiON Battery

    Hi there! Please contact our VP of Customer Experience at bgreen@relionbattery.com and he would be happy to help you with this. Thank you!