Exploring Cell-to-Chassis/Cell-to-Body (CTC/CTB) designs for e-2Ws

India’s Electric two-wheeler market is growing at a rapid pace, averaging about 1 lakh units per month. As customer numbers increase, so does the demand for longer range and better performance. This is why innovation in Battery Pack integration is of key importance. Traditionally, battery packs were over-engineered with a box-in-box-in-box approach for safety reasons. As the technology keeps advancing, we have seen a gradual reduction in these layers, moving towards the futuristic Cell-to-Chassis/Cell-to-Body (C2C/C2B) architecture.

What is C2C/C2B?

Unlike conventional packs, where a group of cells is enclosed in a module that is then assembled into a pack, C2C/C2B or structural battery architectures embed cells directly into the vehicle’s chassis, which can also act as a load-bearing member in some cases. Conventional Battery pack enclosures can account for anywhere between 20% to 30% of the total Battery weight. This pack is then assembled into the vehicle chassis frame.

C2C/C2B packs do not have a separate pack casing. The chassis doubles as the enclosure, and the cells may double as load-bearing members. The reason to mention “may” in the previous sentence is because in some cases, cells are not carrying any loads – CTC, and in some cases, the cells are acting as load-bearing members – CTB. As such, CTB results in what can be called “negative mass,” where a reduction in weight is observed from the main frame due to the cells substituting as load-bearing elements, thereby contributing to structural stiffness and energy absorption. This dual reduction enhances vehicle mass efficiency, improving payload-to-weight ratio while preserving mechanical strength.

We have already seen several C2C/C2B commercial applications in the automotive industry, especially in the passenger car segment, including Tesla, CATL, BYD, XPENG, Leapmotor and Xiaomi. Even though it has gained traction in the e-4W segment, adoption in the two-wheeler (and even e-3W) segment has remained limited, with only a handful of prototypes and concepts presented globally. Yet, this concept holds significant promise for compact vehicle platforms, such as scooters, motorcycles, and e3Ws, where volumetric efficiency and structural synergy are critical.

By eliminating secondary enclosures, C2C/CTB integration can boost ~30% mass reduction and 25 to 40% range increase. Applied to Indian e-scooters, this could potentially add 50–80 km of extra range for the same weight, which is critical for daily commutes and fleet operations.

Manufacturing Considerations

The chassis is the skeleton of a vehicle. It is the underlying framework that supports and connects various vehicle parts, ensuring stability and strength while linking different sections within the vehicle. Therefore, the chassis is traditionally not an energy storage system. As such, implementing C2C/C2B requires a fundamental restructuring of the design from scratch, especially for e-2Ws.

A core element to this strategy is to make custom-casted modular Chassis frames designed to house specific Battery Cells. However, casting such components with high dimensional accuracy is non-trivial. Post-casting machining, integration of sealing features, and surface treatment are critical steps that add manufacturing complexity and cost.

In C2C/CTB, the battery cells are assembled first, making them the foundation of the entire vehicle build. This is in contrast to conventional EV designs, where the vehicle body is built first and battery packs are installed in the final stages. As a result, a PMFEA must be set up not only to ensure the accurate alignment of cells but also to support the downstream assembly of vehicle subsystems, such as suspension, drivetrain, and body panels.

To address this, modular chassis designs are being developed, where the front fork assembly, floor-mounted cell array, and rear sub-frame can be disassembled independently. This modularity improves serviceability and enables safer, more manageable assembly workflows. However, it also requires high repeatability in the joining interfaces and poses structural validation challenges.

At scaled production, worker safety also becomes a challenge in this reversed assembly of e-2Ws as the high-voltage element is placed first, exposing technicians to potential safety hazards. Finally, real-time quality control (QC) becomes essential in high-volume production. Automated inspection systems must verify all the necessary interfaces to ensure the structural and electrical reliability of the integrated chassis-battery system.

Post Manufacturing Challenges in CTC/CTB

One major question raised within the EV industry around CTC/CTB is: What happens in the event of a crash resulting in damage to the chassis?

For conventional vehicles, the battery is closed in a protective box, which is isolated from the load-bearing members of the chassis. In contrast, CTC/CTB puts the cells directly in the path of load-bearing elements or acts as a load-bearing element itself. This means that any chassis damage could potentially compromise the energy storage system, and even if it doesn’t, how do we repair or replace this damaged section? Does this mean that vehicle maintenance will require us to replace the entire chassis and battery?

Addressing these questions requires novel safety approaches—such as crumple zones, cell compartmentalization, and modular chassis frame—to ensure that localized impacts do not require the whole battery frame replacement. These design considerations must be tailored specifically for the particular e-2W.

Current Indian homologation standards, such as AIS 156, govern battery safety for electric two-wheelers but do not yet completely address structural integration. This creates a gap in certification for manufacturers exploring this technology. In the near future, a collaboration between manufacturers and regulatory bodies, such as ARAI and ICAT, will be essential to establish new testing norms for homologating such vehicles, particularly in terms of crashworthiness, thermal events, and maintenance protocols.

Scope Beyond Two-Wheelers: Opportunity in 3W EVs

While this article focuses on two-wheelers, it is worth mentioning that CTC/CTB integration holds significant promise in the growing three-wheeler segment, especially in markets like India, where electric rickshaws and cargo three-wheelers contribute substantially to urban logistics, with sales averaging around 50,000 units monthly. These vehicles often have flat chassis platforms, like e-4W skateboard platforms, making them suitable candidates for structural battery integration. Cell-to-chassis/body battery packs could improve both payload capacity and vehicle stability. e-3W platforms offer a practical middle ground between e-2W and e-4W structural pack constraints, making them a strong candidate for early adoption of CTC/CTB designs in commercial use cases.

Closing Remark

To date, the e-2W CTC/CTB remains largely in the concept stage, with no OEMs having confirmed a fully developed prototype. However, a few companies have begun early-stage development. Ola Electric has showcased its Gen-3 platform concept with battery and powertrain integrated into the vehicle body. XLEX batteries, a deep-tech battery start-up, is working on multiple Cell-to-Chassis and Cell-to-Body concepts for light electric vehicles.

To conclude, Cell-to-Chassis (C2C) / Cell-to-Body(C2B) integration offers a compelling path for India’s EV evolution, catapulting us to the forefront of technology integration. However, its realization hinges on robust engineering, regulatory alignment, and strategic collaboration. As more teams’ pilot C2C/C2B prototypes, the momentum is shifting from concept to reality.

References

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• “Structural Integration of Battery Packs in EVs”, IEEE Access, Vol. 10, 2022.

• “Integrated Structural Battery Design for Lightweight Electric Vehicles”, Composites Part B: Engineering, Elsevier, 2021.

• “EV unit sales in India report” – EVreporter, sourced from eVahan Portal, 2025

• “Electric Two-Wheeler Sales”, Society of Manufacturers of Electric Vehicles (SMEV), June 2024.

• “India Electric Vehicle Market Outlook 2024”, NITI Aayog & Rocky Mountain Institute (RMI), April 2024.

• “Automotive Industry Standard – AIS 156: Requirements for Battery Safety in EVs”, Automotive Research Association of India (ARAI), 2023.

• “Government of India Gazette Notification: Battery Safety Requirements for Electric Vehicles”, Ministry of Road Transport & Highways, 2022

• “Advances in Battery Pack Manufacturing and Assembly”, International Journal of Advanced Manufacturing Technology, Springer, 2022.

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• “Volumetric Efficiency Improvement via Structural Battery Integration”, IDTechEx Report on Structural Batteries, 2023.

• “Crashworthiness of Structural Battery Packs in EVs”, SAE Technical Paper 2020-01-1387, Society of Automotive Engineers, 2020.

• “Battery Enclosure Design for Impact Protection in EVs”, National Renewable Energy Laboratory (NREL), U.S. Department of Energy, 2021.

• “Electric 3-Wheelers in India: Market Landscape and Technical Challenges”, ICCT India Working Paper, July 2023.

• “Electrification of L5 Vehicles in Urban India”, World Bank India EV Technical Series, 2022.

About the author

Pranav Nagaveykar, Founder – XLEX Batteries Pvt Ltd

Pranav has over 12 years of experience in EV battery R&D. He has worked with leading OEMs, including TATA, FORD, and Maserati, and is also involved in solid-state battery research in Paris. At XLEX, he is building a deep-tech battery startup focused on innovative pack architectures, developing structural and immersion-cooled battery technologies specifically for lightweight electric vehicles.

This article was first published in EVreporter July 2025 magazine.

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