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August 29, 2022

Battery Management System for Electric Vehicles

Battery Management System for Electric Vehicles Overview

Automotive companies and legislatures are pushing the boundaries to lower carbon emissions everyday. As a result, electricity is replacing fossil fuel in vehicles at a dizzying rate. In fact, California's Air Resources Board (CARB) recently voted in favor of banning the sale of new gas-powered vehicles in the state by 2035. 

Battery management systems are critical components in any electric system. In this blog, we will explore battery management systems in the automotive industry and how they are used today. 

What is a battery pack?

Battery cells are used to store energy in the chemical form. When required, they convert chemical energy into electrical energy to drive traction motors. Battery packs are a combination of battery cells in series or parallel arrangement. Battery Electric Vehicles (BEVs) rely completely on battery packs for power. 

What is a battery management system?

The most common battery chemistry in the automotive industry is Lithium ion. This cell chemistry is very susceptible to cell temperature and pressure, thus requiring the cells to be operated within a safe operating boundary. To achieve the required performance, prolong the battery life, and mitigate hazardous situations, a supervisory control system is required. This system is known as a Battery Management System (BMS). 

What do battery management systems do?

A BMS battery system comprises electronic hardware and embedded software. The primary function of a BMS is to meet the safety requirements for operating a battery under various load and environmental conditions. This reduces risk during operation. 

More functionality is typically integrated into the BMS design to increase efficiency and to prolong battery life of the individual cells and the pack as a whole. Both of these will directly lower the cost of owning and operating a battery electric vehicle. A battery management system plays an important role in smart battery technology by sensing, controlling and computing the following functions:

  • Cell monitoring
  • Energy recovery
  • ECU (Electronic Control Unit) communications
  • Battery protection
  • Active cell balancing

Cell monitoring

The BMS monitors the state of the battery using the following metrics: 

  • Cell voltage
  • Cell current
  • Cell temperature
  • State of balance
  • Fuel gauge or State-of-Charge (SOC) 
  • Charge holding capacity or State-of-Health
  • State machine outputs including Idle, Discharge, Charge, Fail Safe and Sleep modes

Energy recovery

The BMS will control the recharging of the battery during regenerative braking and redirect the recovered energy back into the battery pack.

ECU communications

The BMS controller will communicate with the Electric Control Unit (ECU) via the CAN bus to conduct the following functions: 

  • Authentication
  • Collection, storage and secure sharing of critical data with other nodes
  • Run battery diagnostics
  • Protect against faults

Battery protection

The BMS will include a battery charging system and protect the battery from operating outside of its safe operating range. It will typically use cut-off FETs to limit battery operation during the following events: 

  • Overcurrent during charge
  • Overcurrent during discharge
  • Overvoltage during charging
  • Undervoltage during discharging

Active cell balancing

The BMS may be used to maximize the battery’s capacity and increase each cell’s longevity by maintaining an equivalent state of charge of every cell. Cell balancing can be either passive or active: 

  • Active balancing: Energy is drawn from the most charged cell and transferred to the least charged cell using DC-DC converters, capacitors or inductors
  • Passive balancing: Energy from the most charged cell is dissipated as heat using resistors

‍See how automotive OEMs are building BMS systems using Collimator today

What are the best car manufacturers doing that others are not?

Anyone who owns an EV has experienced “range anxiety” at least once in their life. This is the fear that their vehicle has insufficient energy to cover the distance needed to get to a charging station. Building out more charging stations is expensive, therefore, better and more sophisticated battery management systems are the way forward. Here are two examples of companies leading the way: 

Tesla uses BMS systems to win the range game

Tesla relies heavily on real world data and modeling and simulation to maximize their vehicle efficiency. For more than 10 years, Tesla has been collecting and analyzing powertrain data to continuously optimize their vehicle parameters. Tesla uses V2X cloud connectivity to get data from vehicles in production. They will combine this data with simulation data to analyze the weakest components from a performance and cost standpoint. 

They will generate insights and use CI / CD to push OTA updates to reduce inefficiency losses and increase the range. As a result, they are estimated to have improved their motor efficiency by 30% over the years. The Tesla Model S now comes with a 100 kWh battery pack yet boasts about having the longest range of any EV in the industry. 

Ather Energy uses battery monitoring system to improve rider experience

Ather Energy is an Indian electric vehicle company. They are “on a mission to revolutionize the electric mobility and commute experience with their efficient and connected intelligent electric scooters”. Ather recently introduced their new flagship 450X Electric Scooter with significant improvements to stay ahead of the increasingly competitive Indian EV market. 

The improvements include a battery management system that maintains the power extracted from the batteries regardless of the temperature, load or terrain. This means that a rider still gets the same level of performance and torque without sacrificing battery range.

Another improvement is the introduction of “ride modes” such as Warp, Sport, Ride and SmartEco. Riders can customize the performance of their batteries based on what they want. For example under the SmartEco mode, riders can maximize the range of the battery. In Warp mode, riders can maximize the horsepower and acceleration of the motors. 

Why use Collimator for BMS design? 

BMS controllers require rigorous testing with battery plant models before they can be integrated with a physical battery and deployed on an actual vehicle. As battery management systems become more sophisticated, system engineers need tools that can match the increased complexity. 

Collimator can do that and more. Collimator is an engineering tool for data driven modeling and simulation of dynamical systems. Collimator has proven instrumental for hundreds of engineers designing battery management systems in the following areas: 

  • Modeling battery and controllers and running hundreds of test cases in simulation environments (e.g. MIL, SIL, HIL testing)
  • Modeling non-linear (analytical, data-driven or hybrid) battery models while leveraging open-source Python based battery libraries (eg. Pybamm) which offer physics-based electrochemical DAE models 
  • Running simulations using high performance computing directly from the user's Python environment. Collimator is a web based app with APIs that can be called from anywhere to run simulations and get results without compromising information security

Find out more about how Collimator can help you build your battery management system by booking a meeting with our application engineering team. 

Frequently Asked Questions

What are the benefits of a BMS?

A battery management system will monitor the state of a battery, its environment and modulate I/O to ensure optimal battery performance and reduce risk. There are different parameters which are tuned to optimize different aspects:

  • Charge and discharge current limits are tuned to reduce heating up of the battery and thereby avoid hazardous situations and increase battery lifespan
  • Charge and discharge current limits are also tuned to improve battery efficiency and hence vehicle range
  • Well tuned fuel gauge meter or SOC estimation results improves accuracy in range prediction and reduces range anxiety

What is a service battery charging system?

A battery charging system is used to control the electrical energy from the car’s alternator. It keeps the charge in the car's battery and provides electrical energy for the car’s systems. Such systems include the lights, windows, radio, etc. 

What kind of batteries are commonly used for EVs?

Batteries function as energy storage systems. Batteries are differentiated by their materials and compositions. The following are the prominent battery types which either have already found applications in EVs or are under research stage due to their potential:

Lithium-Ion Battery

Lithium ion battery packs offer high energy-to-weight ratio, power-to-weight ratio, efficiency, good high-temperature performance, and low self-discharge. Challenges include recycling cost, useful life, and potential hazards from overheating and thermal runaway

Nickel-Metal Hydride Battery

Nickel metal hydride battery packs offer good life cycles, abuse tolerance and are environment friendly. Challenges include cost, self-discharge, specific energy and power constraints, and non linear behavior in high temperature

Nickel-Cadmium Battery

Nickel cadmium batteries offer good lifespans. Challenges include partial charge-discharge cycle performance and toxicity

Sodium-Nickel Chloride Battery

Sodium nickel chloride batteries offer good life cycles and are environment friendly. Challenges include specific power constraints, safety, long-term charge storage and cold weather performance

Lead-Acid Battery

Lead acid batteries offer good cost, safety and reliability. Challenges include cold temperature performance and low lifespans

Solid-state Battery

Solid state batteries offer specific energy and power characteristics. This technology is still in the research stage, however, has shown great promise


Ultracapacitors are commonly used as secondary energy-storage devices. They offer quick power delivery and good storage characteristics. Challenges are primarily cost

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