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What Is A BMS (Battery Management System)?

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Lithium-ion batteries have a lot of advantages over their lead-acid counterparts. They’re lighter, more efficient, charge faster, and have a longer lifespan. However, they’re susceptible to conditions that can damage the battery pack. Tapping into all of this potential requires lithium-ion batteries to be more complex and include components to help avoid these damaging conditions. In fact, this is the primary purpose of the BMS, which means a battery management system.

What is a Battery Management System? 

A battery management system (BMS) is said to be the brain of a battery pack. The BMS is a set of electronics that monitors and manages all of the battery’s performance. Most importantly, it keeps the battery from operating outside of its safety margins.

The battery management system is critical to the battery’s safe operation, overall performance, and longevity. Moreover, it protects whatever the lithium battery is installed in (boat, RV, etc.) and the people who are using it.

family sitting on a blanket while the father plays the guitar

What is the Function of a Battery Management System? 

The primary function of the BMS is to protect the battery cells from damage caused by being overcharged or over-discharged. Additionally, the BMS calculates the remaining charge, monitors the battery’s temperature, monitors the battery’s health and safety by checking for loose connections and internal shorts. The BMS also balances the charge across the cells to keep each cell functioning at maximum capacity.

If it detects any unsafe conditions, the BMS shuts the battery down to protect the lithium-ion cells and the user.

How Does a Battery Management System Work? 

The battery management system monitors individual cells in the battery pack. It then calculates how much current can safely go in (charge) and come out (discharge) without damaging the battery.

The current limits prevent the source (usually a battery charger) and the load (such as an inverter) from overdrawing or overcharging the battery. This protects the battery pack from cell voltages getting too high or low, which helps increase the battery’s longevity.

The BMS also monitors the remaining charge in the battery. It continually tracks the amount of energy entering and exiting the battery pack and monitors cell voltages. It uses this data to know when the battery is drained and shut the battery down. This is why lithium-ion batteries don’t show signs of dying like a lead-acid, but just shut off.   

Why a BMS is Important

Battery management systems are critical in protecting the battery’s health and longevity but even more important from a safety perspective. The liquid electrolyte in lithium-ion batteries is highly flammable.

So, these batteries need to be operating optimally and within safety limits at all times to prevent a fire.   

Battle Born Built-In Battery Management System

All Battle Born Batteries have a built-in BMS. This protects against all of the most common causes of battery failures and dangers.

These include protecting the cells against short circuits, high currents, excessive heat, cold, and high or low voltages. Battle Born’s built-in BMS also protects against faults.  

Learn All About Battle Born’s Battery Management System here.

battle born batteries 100Ah 12V LiFePO4 Battery

Protections Offered By a Battery Management System

Let’s review the protections of a battery management system:

Under and Over-Voltage

Damage occurs if you overcharge (cell voltage getting too high) or over-discharge (cell voltage gets too low) a lithium-ion battery cell. The BMS helps protect from under and over-voltage situations so that damage to the battery’s cells does not occur.

Temperature Extremes

The safety and stability of lithium-ion battery cells depend on temperature maintenance within certain limits. If the temperature exceeds the critical level on either end, thermal runaway can occur. Consequently, this can lead to an inextinguishable fire.

The BMS monitors the temperature and sometimes controls cooling fans (in the case of an electric vehicle) to help maintain proper conditions. It will even shut down cells if needed to protect the battery.

Protection from Shorts

Internal and external shorts can also lead to thermal runaway. For this reason, protection from shorts is another critical component of a battery management system.

What a battery management system does graphic

Keep Your Batteries and Your Family Safe With a BMS

There are many benefits to lithium-ion battery technology. But lithium-ion battery cells and conditions must be monitored, managed, and balanced to ensure safety and optimal longevity and efficiency.

The battery management system is the primary component in the battery pack that monitors all of these conditions. Above all, it keeps your batteries operating safely and optimally so you can get out there and stay out there with peace of mind.

man sunbathing on the front of a sailboat

Want To Learn More About Electrical Systems and Lithium Batteries?

We know that building or upgrading an electrical system can be overwhelming, so we’re here to help. Our Reno, Nevada-based sales and customer service team is standing by at (855) 292-2831 to take your questions!

Also, join us on Facebook, Instagram, and YouTube to learn more about how lithium battery systems can power your lifestyle, see how others have built their systems, and gain the confidence to get out there and stay out there.

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10 thoughts on “What Is A BMS (Battery Management System)?

  1. With LiFePO4 battery packs based on “cylindrical cells (e.g. 26650 type cells that look like a flashlight D-cell)”, I often see the recurring comment “The battery management system monitors individual cells in the battery pack.”

    Isn’t it more the case that Battle Born and others wire ~30 26650 “cells” in parallel to form a bank, and then wire 4 banks in series to complete the battery pack? And while there are 120 26650 “cells” in the battery pack, the BMS only monitors and balances the 4 banks (of 30 cells each)?

    I wonder if some of the misleading terminology comes from LiFePO4 batteries based on “prismatic cells” (the cells look like a brick or cigar box) where only 4 prismatic cells are required to complete a battery pack, and the BMS only monitors those 4 prismatic cells (banks).

    The two 100Ah Battle Borns in my camper have been awesome, and I thank Battle Born once again for the phone support when I installed them last year.

    1. Hi Richard, thank you for reaching out. In extreme situations, the BMS does not rely on electricity to solely function, and we have not tested for scenarios like this. If you have any additional questions please feel free to give our technical sales team a call at 855-292-2831.

  2. 1) How can the Internal Circuitry for the Battery Management System (“BMS”) be tested in the Field?
    2) How can Customer determine if the BMS is operational and in safe condition in any particular Battle Born LiFePo(4) Battery?
    3) If two (2) Battle Born LiFePo(4) Batteries of the same type (with BMS) are installed in parallel, will/could the individual BMS internal circuit systems interfere with each other? (e.g. provide a “false-fault” )?
    4) If one BMS is malfunctioning in one Battle Born LiFePo(4) Battery, will it affect the BMS in the other?
    5) If any/either BMS is malfunctioning, will it affect the operation of any Charging/Inverter system?

    1. Hi Gary! If the BMS on your battery has shut it down, we recommend jumping it with another 12V source. Just connect your Battle Born battery to a starting battery from a boat or car, and jump like you would a car battery, leaving them connected for a few minutes and up to an hour. This should wake up the Battle Born Battery, and if you have a voltmeter, you should be able to read a voltage above 10V coming from the battery. Then you can charge it normally.

  3. Hi. I have 4 BB 100 amp batteries I want to install in my motorhome. I have a diode battery isolator built in which of course does not sense voltage from the alternator. I assume the BMS will not allow charging if it is full. Is that correct? My next assumption is if the BMS shuts of charging it will not allow current to flow to the house 12Volt electrical system. Or will the BMS allow outflow of current from the batteries to the devices?

    Thank you

    1. Hi Richard. When connecting your alternator to charge your house bank, we recommend using a DC-to-DC charger in between to help protect your alternator.

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