1. Cell-to-Module (CTM) – The Old Way

Under the hood of older EVs (think first-generation Nissan Leaf, Chevy Bolt, early Tesla Model S/X, etc.), you’d find the CTM style battery. Engineers of the 2010s spread cells out into modules so they could manage them piece by piece. This modular method ⇱ let car makers mix-and-match capacity easily. For example, adding a module is like adding another row of batteries to increase range. Volkswagen’s MEB-platform cars (like the ID.3) famously use a common pack case and change range by plugging in more or fewer modules.

But imagine carrying all those cartons around: each one has steel covers, brackets, and empty space. That’s extra dead weight. It also makes the pack larger and heavier. You end up building extra structure into the pack and under the car to hold those modules. In short, CTM was reliable but not super space-efficient and energy efficient.

Key takeaways (CTM):

• Pros: Easier pack thermal/control design; flexible capacity sizing (e.g. VW ID modules); proven battery technology.

• Cons: Lots of extra parts (module walls, frames); lower energy density ⇱ (modules eat space); heavier packs.

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CTM remains a sensible choice where serviceability, easy repair and spare-part logistics matter (fleet, retrofit and low-volume vehicles). However, CTP and structural options are displacing CTM in many passenger EV and high-volume programs because they deliver better pack density and lower assembly cost per kWh.

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2. Cell-to-Pack (CTP) – Skipping the Middleman

In the race for more range, engineers cut out the middle stage. Cell-to-Pack (CTP) means no modules. Instead of placing cells into boxes first, all the cells are bolted or glued directly into the big pack housing. It’s like dumping the eggs straight into one giant crate without cartons. Many modern EV battery packs ⇱ use CTP: you’ll see long prismatic or pouch cells laid out side by side in the pack case, often with cooling plates in between.

This design packs in more “active” battery material for the same volume. Motor1 explains that CTP packs have a higher percentage of active cells than modular packs. The bottom line: more kilowatt-hours per liter. You get greater energy density and hence longer range without increasing pack size. The Business Wire industry report notes that almost half of new EV models in 2023 had CTP packs ⇱, a dramatic rise from only 13 models in 2021.

Real companies using CTP include battery giants and automakers. Tesla’s new 4680 packs ⇱ are built this way – its cylindrical cells are laid “in one uniform, unbroken expanse” inside the pack. CATL (a leading Chinese battery supplier) sells CTP packs like the Qilin battery, which fit cells directly into the housing. Even BYD’s Blade battery technically skips modules: its iron-phosphate cells lie flat and form a structural “sandwich” inside the pack.

The advantages of CTP are clear:

• Higher energy density: More room for cells means more kWh, boosting range.

• Less hardware: Fewer parts and welds means lighter packs and simpler assembly.

• Lower cost (potentially): With fewer module frames and connectors, materials cost drops, and manufacturing is faster (no module assembly steps).

There are trade-offs, though. Removing modules means the pack has to serve all functions by itself. Engineers must design new support structures so cells don’t bounce or overheat without the module shell. Thermal management system and crash safety become more challenging (you need strong adhesives or potting, as HB Fuller points out). But overall, CTP is a big step forward in squeezing more energy into the same space.

For custom EV projects, however, the most advanced architecture is not always the most practical choice. Packaging space, repairability, production volume, thermal management and development cost should be evaluated together before selecting a battery architecture.

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Since 2023–24 CTP adoption accelerated: the global CTP market expanded rapidly and is forecast to keep double-digit growth as OEMs and battery suppliers use CTP to raise pack volumetric efficiency and simplify assembly. Major suppliers (CATL, BYD and some OEMs) now offer CTP-style products and several manufacturers have certified CTP packs to new national safety standards.

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3. Cell-to-Body (CTB) – Battery as Part of the Car

Pushing the idea further, some automakers have baked the battery into the electric vehicle (EV) body itself. That’s Cell-to-Body (CTB) ⇱(sometimes called Cell-to-Chassis), where the cells attach directly to the car’s underbody instead of a separate pack frame. Imagine the car’s floor pan is made of battery cells.

In a CTB design, there’s no traditional battery “box” at all. The floor or chassis is built to hold the cells, which are bonded or fastened straight to the car’s skeleton. The World Economic Forum describes CTB as installing cells “into the car’s body” to save weight and space. BYD’s new Blade battery is a prime example: in the BYD Seal ⇱ and Han EVs, the blade cells lie flat under the floor, and the pack’s covers double as body panels. The cells aren’t just inside the chassis; they are the chassis in that area. Motor1 notes that in a CTB setup, the battery “performs a real structural function” – it adds rigidity and links parts of the frame together.

What do you get by doing this? Several wins:

• Even more space & lower weight: There’s no separate pack box to store, and no heavy module frames. As the WEF explains, integrating cells into the body “reduces the weight of the vehicle and frees up space”. You don’t need extra steel for a battery casing because the chassis itself holds the cells.

• Stiffer, safer body: Since the battery becomes part of the car’s skeleton, the chassis is very rigid. Tesla’s engineers call this cell-integrated approach a structural battery pack ⇱ – it helps the car resist twisting forces. One expert notes that in a CTB/CTC design ⇱, the battery is a key load-bearing member of the chassis. This extra stiffness can improve handling and crash safety (more on that below).

• Simpler assembly: With cells attached directly to the floor, building the pack is faster. You literally glue or bolt cells onto the car in one step, instead of first assembling modules. According to Wired, “cells and the chassis become multi-purpose,” which simplifies the build and “turns [battery casing] from dead weight into something valuable to the structure”. In plain terms, fewer parts and fewer assembly steps = cheaper, quicker production.

Real-world CTB: BYD blazed the trail here. Its 2022 Seal sedan was the first production EV to use a full CTB design. In BYD’s packing, the blade cells literally replace a portion of the floor plate. The result is impressive: BYD reports a 66% volume utilization (more of the space is active battery) and a super-rigid body (torsional stiffness >40,000 Nm). The Seal’s body is so tight and well-integrated that it has a drag coefficient of just 0.219 (very slick shape!) and can sprint 0–100 km/h in only 3.8 seconds, all while sipping just 12.7 kWh per 100 km. Those gains come from the efficient packaging and light weight of the CTB battery.

Other automakers are following suit. Xpeng’s new “Fuyao” (Glacier) platform uses a CTB-like approach: the battery pack top cover is also the car’s floor, saving 5% of vertical space inside the cabin. Seats can even bolt right onto the battery cover, treating the pack as part of the interior floor. Many call Tesla’s next-gen EV battery pack design “cell-to-chassis,” which is essentially the same idea: Tesla showed a future Roadster/Cybertruck frame where the battery is built into the chassis rails. The Tesla team claims this cell-to-chassis tech can cut ~10% of vehicle weight and boost range by ~14%, plus it slashes hundreds of parts (they estimate ~370 fewer components).

Key takeaways (CTB/CTC):

• Pros: Drastic weight and space savings; ultra-low floor & more cabin room; extremely rigid chassis; fewer parts and faster builds. A CTB car can feel more solid, go farther on each charge, and even have extra legroom or storage space.

• Cons: Requires very safe cells (they live in the car structure); engineering challenges (cooling and crash protection are critical since the battery is exposed); tooling costs. Also, integrating the pack with the car means the battery supplier loses some control, which can cause industry pushback.

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4. Regulatory & safety updates (2024–2026)

• China’s GB 38031-2025 (the “no fire/no explosion ⇱” standard) published in 2025 and being phased in — battery makers are certifying new pack designs to meet it; CATL was an early passer.

• EU Battery Regulation (Regulation (EU) 2023/1542) is in force and adds CE-type requirements, digital battery passports, and recycled-content / recycling-efficiency targets affecting pack design and lifecycle planning.

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5. Why It Matters: Comfort, Performance, and Production

These futuristic layouts aren’t just buzzwords – they bring real-world benefits to drivers and builders. Here’s how cutting-edge pack design helps you:

• More driving range: By squeezing out non-energy parts, newer designs pack in more cells. CTP and CTB electric vehicle batteries can store more energy in the same space. Tesla says its cell-to-chassis pack could boost range ~14% over today’s design. That’s extra distance on every charge.

• Faster acceleration and efficiency: A lighter, stiffer car can launch quicker and use energy better. BYD’s CTB Seal is a good example – it’s a compact sedan that rockets 0–100 km/h in just 3.8 seconds, thanks partly to its high-tech battery pack. Meanwhile, the same structure lowers air drag and rolling resistance, so it sips just 12.7 kWh/100 km.

• Roomier cabin: Without bulky battery boxes, engineers can lower the floor. CTB/CTC layouts often mean a flat, reinforced floor pan. Xpeng claims about 5% more headroom/space by using a pack cover as floor. Fewer hump and less wheel-tunnel intrusion can make the interior feel bigger. Plus, with less dead weight, the car’s suspension can be tuned more softly for comfort.

• Better ride and safety: A stiffer chassis means the car handles bumps and corners more crisply, giving a solid, stable feel. Crash performance can improve too: if the battery pack is part of the crumple zones, engineers can ensure the crush structure and batteries are more intelligently designed. For example, Tesla noted its new pack ⇱ lets it extend the battery “further” front and back, creating better crumple zones in a crash. (Think of it like having a stronger spine and built-in airbags along the car’s bottom.)

• Cheaper and faster builds: On the factory line, simpler is better. Cell-to-pack and cell-to-body designs mean fewer parts to bolt together. As one industry blog explains, cutting out modules trims the parts list drastically. Tesla’s structural pack reduces part count by 370 pieces, which can cut manufacturing time and cost. With modules out of the picture, the entire pack can be assembled in fewer steps, saving labor. WEF even notes that integrating cells into the body “makes for simpler assembly” and uses fewer materials. In short, the car can be built more like one big piece than a jigsaw puzzle – cheaper for companies and, eventually, possibly cheaper for buyers.

However, every upside has a trade-off. Newer tech forces tougher safety requirements. Cell-to-body designs need batteries with rock-solid stability, since the cells are part of the car’s structure. They also require rethought cooling and fire protection (with no module cases to contain a cell). But engineers are solving these with new materials (like fire-blocking epoxies and stronger adhesives) and better cell chemistries.

The bottom line: By getting creative with how cells, modules, and packs fit together, EV makers are cheating the laws of physics a bit. They pack more juice into each square inch while trimming weight and cost. For drivers, that means longer trips, quicker acceleration, and even a smoother ride. For manufacturers, it means catching up to ICE cars in affordability and comfort.

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Note: The above is a simplified summary. Many modern EVs combine elements (for instance, BYD’s Blade cells are CTP in design but glued to the body for CTB integration). The trend is clearly toward skipping modules and even pack enclosures to push energy density and efficiency to the max.

Liquid cooling plates remain the mainstream choice for high-power and fast-charge packs because they offer predictable temperature control and scalable manufacturing. At the same time, passive and hybrid strategies (phase-change materials, nano-enhanced PCMs and immersion cooling) are moving from R&D to pilot projects for specific use cases where packaging or safety benefits are prioritized. Match your thermal approach to cell format, C-rate targets and vehicle duty cycle.

In short: CTM = the old faithful (modules inside pack). CTP = modern high-density packs (cells straight into pack). CTB/CTC = cutting-edge – the battery is part of the car’s bones. Each step up (CTP → CTB/CTC) lets us use battery cells more wisely, boosting range and saving weight. This translates to more comfort (roomier cabin, lower floor, stiffer ride), high performance (lighter car, longer range, stronger chassis), and faster production (fewer parts to assemble).

Bottom line: EV battery ⇱ tech is advancing fast. By the time new EVs hit the road, cell-to-pack and cell-to-body designs will likely be the norm. That means your next EV could be lighter, drive farther, and cost less – all because of clever packaging inside the pack. Keep an eye on your favorite brands: if they talk about structural batteries or integrated packs, that’s just geek-speak for “we’re skipping the boxes and making your battery part of the car!”

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6. Choosing the Right EV Battery Pack Architecture for Your Project

CTM, CTP and CTB/CTC technologies each have clear advantages, but the newest battery architecture is not automatically the best choice for every electric vehicle project.

For mass-produced passenger EV platforms, CTP and structural battery designs can improve packaging efficiency and reduce non-active components. However, these architectures normally require deeper integration between the battery, vehicle chassis, thermal system and manufacturing process.

For EV conversions, specialty vehicles, commercial vehicles, prototypes and lower-volume OEM projects, a custom modular or semi-integrated battery pack may often provide a better balance between packaging efficiency, serviceability, development cost and production flexibility.

When evaluating an EV battery pack, the following engineering requirements should be considered together:

6.1 System Voltage

Battery voltage must match the operating voltage range of the motor controller, charger and other high-voltage components. Common EV battery platforms may range from 48V and 72V systems for light electric vehicles to 96V, 144V, 300V, 400V or higher-voltage systems for more powerful applications.

6.2 Required Energy and Driving Range

Battery capacity should be calculated according to the vehicle’s expected energy consumption, operating time and required driving range rather than selecting Ah or kWh independently.

6.3 Available Installation Space

Maximum battery length, width and height often determine cell format, cell arrangement and pack architecture. For custom EV projects, packaging design can be just as important as battery capacity.

6.4 Continuous and Peak Current

The battery, BMS, busbars, contactors, connectors and cables must all be designed around the motor controller’s continuous current and short-duration peak current requirements.

6.5 Thermal Management and Operating Environment

Ambient temperature, discharge rate, charging rate and vehicle duty cycle determine whether passive cooling, air cooling, liquid cooling or heating functions should be considered.

6.6 BMS and Vehicle Communication

CAN communication between the battery BMS, vehicle controller, display, charger and other components should be defined early in the project. Communication protocol, baud rate and required CAN messages can affect system integration.

There is no universal “best” EV battery architecture. The most suitable solution is the one that meets the vehicle’s electrical requirements, installation space, safety targets, production volume and budget with the lowest overall engineering risk.

Bonnen Battery develops customized EV battery systems according to these requirements. If you provide your vehicle information, motor/controller specifications and available battery space, our engineering team can help evaluate an appropriate battery solution.

7. FAQs

Q1: What is the main difference between CTM and CTP battery designs?

Compared to traditional Cell-to-Module (CTM) designs, Cell-to-Pack (CTP) technology eliminates the intermediate module stage, directly integrating cells into the pack to reduce weight and complexity.

Q2: How much space does CTP technology actually save in an EV?

According to industry data, switching to a CTP design can increase battery pack volume utilization by 15% to 20%, allowing for more active battery material within the same physical footprint.

Q3: What makes BYD’s CTB technology different from regular battery packs?

BYD CTB (Cell-to-Body) technology refers to an architecture where the battery cells act as a structural part of the vehicle’s floor, effectively merging the battery and the chassis into one solid unit.

Q4: Does integrating the battery into the chassis improve car safety?

Yes, Cell-to-Chassis (CTC) structural integrity is significantly higher than traditional setups; for instance, vehicles using this tech can achieve a torsional stiffness exceeding 40,000 Nm, which greatly enhances crash safety.

Q5: Why is ‘Volume Utilization Rate’ such a big deal for LFP batteries?

Since LFP cells have lower gravimetric density than NCM, a high LFP blade battery volume utilization rate—often reaching 66% in advanced CTB designs—is critical to achieving a competitive driving range.

Q6: What are the primary EV battery pack lightweight design strategies used today?

Modern lightweighting strategies involve three key steps: first, removing non-active module components; second, using high-strength aluminum or composite casings; and third, adopting Cell-to-Body (CTB) integration to eliminate redundant structural steel.

Q7: Is thermal management harder in a module-less battery pack?

Thermal management in CTP packs is actually more efficient because it allows for larger, continuous cooling plates that cover more cell surface area, rather than having individual cooling loops for each module.

Q8: What is the benefit of moving to an 800V high-voltage battery system?

The benefits of 800V high-voltage battery systems include a 50% reduction in charging time and lower heat losses, as higher voltage allows for lower current flow through the vehicle’s wiring.

Q9: How does skipping the module stage affect manufacturing efficiency?

Transitioning to module-less manufacturing can boost production efficiency by approximately 50%, as it significantly reduces the number of parts to be assembled and the complexity of the high-voltage wiring harness.

Q10: Does a Cell-to-Body (CTB) design affect the interior space of the car?

By integrating cells into the body structure, CTB designs can lower the vehicle floor height by 10mm or more, creating significantly more vertical legroom and cabin space for passengers.

Q11: What is the ‘egg carton’ analogy for battery packs?

In battery engineering, Cell-to-Module (CTM) is like eggs in cartons inside a crate; Cell-to-Pack (CTP) is like removing the cartons and filling the crate directly with eggs to maximize every inch of space.

Q12: Is a CTC (Cell-to-Chassis) battery harder to repair?

Compared to modular designs, CTC and CTB architectures are more difficult to repair at the cell level because the battery is a permanent structural component of the vehicle’s chassis.

Q13: How does torsional stiffness benefit EV performance?

A high torsional stiffness (e.g., 40,000 Nm/degree) in integrated battery designs minimizes body deformation during cornering, which leads to sharper handling and a more premium driving experience.

Q14: What are ‘non-active’ elements in a battery pack?

Non-active elements include module walls, internal bolts, and connectors that provide structure but do not store energy; reducing these is the fastest way to increase a pack’s energy density.

Q15: What is the future trend for EV battery housing?

The industry trend is moving toward ‘Ultimate Design’, where the battery casing is no longer a separate box but is fully integrated into the vehicle’s aerodynamic underbody and structural safety cage.

Q16: How do engineers prevent thermal runaway in highly integrated packs?

Engineers use multi-layer protection: including intumescent fire-retardant coatings that expand 50x when heated and specialized pressure-relief vents to channel hot gases safely out of the integrated chassis.

Q17: Can CTP technology be used with all types of battery cells?

While most common with Prismatic and Blade cells, CTP technology is increasingly being adapted for Large Cylindrical cells (like the 4680) to maximize packing efficiency and structural strength.

Q18: What information is needed to design a custom EV battery pack?

To evaluate a custom EV battery pack, engineers normally need the vehicle type, target battery voltage, required capacity or driving range, available installation space, continuous and peak current, charging requirements, operating temperature and communication requirements such as CAN. Motor and controller specifications are also helpful if the final battery requirements have not yet been determined.

Q19: Can an EV battery pack be customized to fit a limited battery compartment?

Yes. For many EV conversion and specialty vehicle projects, the battery enclosure and internal cell layout can be designed around the available installation space. Providing the maximum battery length, width and height allows engineers to evaluate suitable cell arrangements, pack capacity, cooling, BMS and structural requirements.

Q20: Can Bonnen Battery design a battery pack based on my motor and controller specifications?

Yes. If the final battery specification has not yet been defined, you can provide the motor voltage and power, controller operating voltage range, continuous and peak current, expected operating time, available battery space and vehicle application. These parameters can be used as the starting point for evaluating the battery voltage, capacity, discharge capability and pack configuration.