Converting to Electric: What You Need to Know About Battery Selection

Introduction

Choosing the right battery for an electric vehicle (EV) conversion is one of the most important decisions to make as it affects the vehicle's performance, range, and longevity. Advances in lithium-ion technology, including batteries such as NMC, NCA, LFP, and LTO (discussed in the Battery Technologies article), provide distinct advantages for various types of EV conversions. In this post, we look at the important elements to consider when selecting the best battery for your conversion, based on the type of vehicle, to help you make an informed selection that matches your individual needs.

Key factors to consider when choosing the correct battery

The following factors determine the viability of the battery types mentioned above for various use cases. 

Range and Space Considerations

The capacity of the battery determines the range of an EV. A battery’s capacity is determined by its energy density (specific energy) or the amount of charge per unit of mass it can hold. The higher the energy density, the less space is needed to adapt a battery to the chassis of the existing vehicle. This is a vital part of the decision-making process as the available space in the vehicle will limit the range and energy density of the battery's chemistry. 

Power Requirements

The power required to move the vehicle is key in sizing the battery. Can the battery provide enough power to the motor to move the vehicle at maximum load and gradient? This is core to the efficacy of the conversion project. This parameter is commonly known as the specific power of the battery. Different battery chemistries have different specific power characteristics, meaning that the type of battery needed will depend on the needs of each type of vehicle. 

Cost

Different battery technologies come at various price points. With varying consumer preferences and vehicle requirements, the cost of conversion may change drastically. Cost versus conversion viability is central to the conversion process, with the battery being the biggest factor. The battery is the largest, heaviest, and most importantly, the costliest component of an EV. Is the conversion economical based on the type of vehicle being converted and the use-case scenario?

Safety and Thermal Considerations

Safety is paramount when converting a vehicle to an EV. With motors requiring such high power, heat becomes a major concern as Lithium-ion batteries are susceptible to thermal runaway. Thermal runaway occurs when the heat produced by the battery exceeds the amount of heat being dissipated, causing rapid chemical reactions where the battery temperature and current begin to rise rapidly [1]. This, if not handled correctly, will result in a fire or the release of toxic/flammable gasses [1]. The susceptibility of batteries to thermal runaway depends on their chemical makeup and use-case scenarios. Some battery types may also require more complex battery management systems (BMS). 

Lifespan

The lifespan of a battery is defined as its cycle life. Cycle life is generally considered the number of charge and discharge cycles required before the battery degrades to 80% of its original maximum capacity. A battery’s lifespan affects how the EV will be used and limits its economic viability. For example, the longer the battery’s lifespan, the longer the time before battery replacement is required, potentially leading to lower overall costs.

Charging speed

The charging speed of a battery depends on the battery’s chemical makeup and directly influences how an EV is used. Charging speed is measured by the charging C-rate of a battery. Faster charging times lead to less downtime for an EV and may, for example, allow for reduced battery pack size and weight. Increasing charging time may also reduce range anxiety for users. 

Battery considerations by the type of vehicle 

The decision to use what type of battery for what application can be tricky. Below we implement multi-criteria decision making (MCDM) using normalized decision matrices for multiple vehicle types: passenger vehicles, sports cars, light commercial vehicles, heavy-duty vehicles, and specialty vehicles [5]. 

Passenger Vehicles

Passenger vehicles are the smallest and most common vehicle in the EV industry. Their smaller size and demand make them one of the most cost-effective and viable candidates for conversion. There, however, is a need for increased range to cater for long commutes or long-distance travel, despite a smaller chassis. The actual cost of the battery is less important than larger vehicles due to the smaller battery size. Passenger vehicles also necessitate higher safety concerns. Due to the various environments and working conditions these vehicles will be exposed to, there is an increased need for batteries that operate in a wider temperature range. 

The LFP battery chemistry comes out to be the best option for passenger vehicles. NMC batteries are a close second and may be preferred for extending the range of the specific vehicle being converted.

Sports Cars

Sports cars are a little different than passenger vehicles. Sports cars have limited space just like passenger cars, likely even less, but they require more power and torque to match their fun ICE driving experience. For these reasons, a high energy density and specific power battery is required. These cars are not driven very often on average so that they can have lower charging speeds. Sports cars are usually driven in the summer when the weather is warm and dry, so the operating temperature range is smaller. On the other hand, driving sports cars hard during hot summer days could cause overheating and safety issues. 

LFP batteries come out on top again for sports cars, with NMC being a close second. Since sports cars are even smaller than passenger vehicles, using NMC for more range in certain cases may be more practical. 

Light Commercial Vehicles

Light commercial vehicles are vehicles like pickup trucks and delivery vans used for commercial purposes. These vehicles must be safe and reliable while providing enough power to tow loads. There is also significantly more room for batteries than for most passenger vehicles and sports cars so that more cells can be packed into the chassis. The batteries for these vehicles will endure deep cycling, so cycle life is important. Charging can be done overnight as the vehicles depend on longer range and usually only charge at the end of the day. 

LFP batteries come out on top once again. The high specific power, safety, and cycle life make the LFP battery type a clear winner for light commercial vehicles. 

Heavy-Duty Vehicles

Heavy-duty vehicles include buses, large trucks, and garbage trucks; vehicles with massive load capacities. Vehicles like these can get away with lower energy density and lower specific power battery types since they are so large and have room for more cells. The range of these vehicles does not necessarily need to be large either because they often follow similar routes or return to a “home base” frequently. On the other hand, safety and reliability are key considerations. These vehicles get abused by how often and how long they are used, and are driven in a wide range of temperatures in many areas. Therefore, a battery with an excellent safety rating, long cycle life, and fast rechargeability are crucial. 

LFP batteries are the best for heavy-duty vehicles. LFP beats out LTO batteries due to lower costs and higher energy density. 

Specialty Vehicles

Specialty vehicles include construction machinery, forklifts, and agricultural equipment, often used in industrial environments. These vehicles typically have more room for batteries but demand high power output due to their heavy loads and rugged use. Safety and reliability are critical as they operate in various harsh conditions and are used frequently. Unlike passenger vehicles, the range isn’t usually a top priority because they often operate within limited areas or designated work sites. However, batteries must be extremely durable and capable of withstanding extreme temperatures, vibrations, and continuous operation. Fast charging is important to minimize downtime, especially in high-demand industrial environments.

LFP beats out LTO for specialty vehicles. LTO may be preferred in cases where safety is extremely important, or temperatures are extremely high to combat thermal issues.

Conclusion

In conclusion, selecting the right battery for your electric vehicle (EV) conversion is a crucial decision that significantly impacts your vehicle's performance, range, and safety. Each battery chemistry—NMC, NCA, LFP, or LTO—offers unique advantages that cater to different vehicle types and use cases. The LFP battery emerges as the most suitable choice for passenger vehicles due to its balance of safety, cost, and cycle life. Similarly, for sports cars and heavy-duty vehicles, LFP again leads, offering high power output and safety. However, NMC could be preferred for vehicles where range is critical. Overall, understanding the specific requirements of your vehicle type and how different battery chemistries address these needs is key to a successful conversion. By carefully considering factors like energy density, specific power, cost, thermal management, and lifespan, you can ensure your EV conversion is efficient and cost-effective.

BlueForce’s Perspective 

At BlueForce, safety is of the utmost priority. Whenever we are faced with the challenge of converting vehicles, we want to ensure that our clients have confidence that our conversions are safe and reliable. This is why many of our conversions use LFP batteries, which provide the best safety benefits from all the current battery technologies for EVs. Also, LFP batteries are some of the longest-lasting in the EV market, meaning that our conversions will keep vehicles running reliably for a long time. 

References 

[1] Everything PE Editorial Team, “What is a Lithium-Ion Battery? - everything PE,” Everythingpe.com, 2023. https://www.everythingpe.com/community/what-is-a-lithium-ion-battery

[2] Battery University, “BU-205: Types of Lithium-ion,” Battery University, Sep. 18, 2010. https://batteryuniversity.com/article/bu-205-types-of-lithium-ion

[3] S. Shahid and M. Agelin-Chaab, “A review of thermal runaway prevention and mitigation strategies for lithium-ion batteries,” Energy Conversion and Management: X, vol. 16, p. 100310, Dec. 2022, doi: https://doi.org/10.1016/j.ecmx.2022.100310.

[4] Y. Miao, P. Hynan, A. von Jouanne, and A. Yokochi, “Current Li-Ion Battery Technologies in Electric Vehicles and Opportunities for Advancements,” Energies, vol. 12, no. 6, p. 1074, Mar. 2019, doi: https://doi.org/10.3390/en12061074.

[5] M. K. Loganathan, B. Mishra, C. M. Tan, T. Kongsvik, and R. N. Rai, “Multi-criteria decision making (MCDM) for the selection of Li-ion batteries used in electric vehicles (EVs),” Materials Today: Proceedings, vol. 41, pp. 1073–1077, 2021, doi: https://doi.org/10.1016/j.matpr.2020.07.179.

[6] L. Najman, “Why We’re Excited about LFP Batteries for Electric Cars,” Recurrentauto.com, May 31, 2024. https://www.recurrentauto.com/research/lfp-battery-in-your-next-ev-tesla-and-others-say-yes#:~:text=Benefits%20of%20LFP%20Batteries&text=LFP%20batteries%20are%20cheaper%20to (accessed Sep. 25, 2024).

[7] M. Ghamami, “Commercialization of Lithium Titanate Batteries,” 2022.