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Battery Sizing for Classic Car EV Conversions: How Refined Motor Co. Determines Your 200-300 km WLTP Range

  • ryanwan4
  • Jun 15
  • 6 min read

Updated: 2 days ago

When people ask how far a converted classic car can travel on a single charge, the honest answer is: it depends on the battery, and the battery depends on the car. A well-engineered classic car EV conversion will typically deliver 200-300 km on the WLTP cycle, but arriving at that figure is a precise engineering exercise, not a sales promise. The available physical space inside the vehicle and the weight budget that keeps handling safe are the two factors that ultimately set the ceiling. Everything else in the design flows from those constraints.


TL;DR


  • A converted classic car typically achieves 200-300 km WLTP range, determined primarily by battery capacity, which is constrained by available space and vehicle weight limits.

  • Battery sizing is not one-size-fits-all: each classic platform requires individual assessment of its chassis, weight distribution, and usable cavities.

  • Modular battery architecture, like that used by Refined Motor Co., allows capacity to be tailored precisely to each vehicle without compromising its structure or character.

  • Motor technology matters too: axial flux motors are entering the classic car modernization space and allow more efficient use of the available energy budget.

  • Road legality is non-negotiable; battery placement and sizing must meet regulatory standards, not just performance targets.


About the Author


Refined Motor Co. is Hong Kong's leading road-legal electric vehicle conversion specialist, operating at the intersection of classic car preservation and modern drivetrain engineering. The company's in-house team of engineers has built its battery sizing methodology around its own modular battery system, designed specifically for the dimensional and weight realities of vintage platforms



.



Why Does Battery Sizing Matter More Than Battery Brand?


The starting point for any serious discussion of classic car EV conversion range is capacity, measured in kilowatt-hours (kWh). The capacity you install dictates how far the car travels, but you cannot simply install the largest pack available. The battery has to physically fit the car and stay within a safe weight envelope.


"You're always going to need the big four: the motor, the motor inverter, the battery pack, and the charger."

Of those four, the battery pack is the most dimensional constraint. For context, a 26.5 kWh pack can be built from a combination of individual battery modules with varying form factors [1]. The physical shape of each module determines where it can be placed in a given chassis. A long, narrow module may fit perfectly in a transmission tunnel; a compact square module may suit a rear boot floor. Getting the geometry right matters far more than the source of the components.



How Does Physical Space Inside a Classic Car Define the Range?


Building on the capacity argument above, the harder question is not how much energy you want, but how much the car can accommodate. Vintage platforms were not designed with battery packaging in mind. Their chassis members, fuel tank recesses, and floor pans create irregular cavities that must be mapped in detail before any capacity figure is confirmed [3].


Refined Motor Co. approaches this with a structured assessment process:


  • Dimensional survey: Identifying every usable cavity in the chassis, including transmission tunnels, boot floors, and areas beneath seats.

  • CAD modelling: Translating those cavities into a battery box design that maximises capacity without cutting into structural members [3] [5].

  • Modular allocation: Distributing modular battery units across multiple locations to balance weight front-to-rear, not just to maximise total kWh [5].


The result of this process determines the achievable range. If the platform can house a larger pack, range trends toward the upper end of the 200-300 km WLTP window. If the chassis is compact or heavy, the pack is sized accordingly and the range sits toward the lower end of that band. Neither outcome is a failure; both are honest engineering.



What Role Does Vehicle Weight Play in the Range Equation?


A related but distinct question is weight. Adding battery mass to a vintage chassis that was engineered for a much lighter petrol drivetrain changes its handling, braking geometry, and tyre loading. Responsible vintage car electric conversion work treats the weight budget as a hard constraint, not a variable to push.


Factor

Effect on Battery Sizing Decision

Original kerb weight

Sets the ceiling for total added mass, including battery and motor

Front/rear weight split

Governs how battery modules are distributed across chassis cavities

Suspension rating

Limits how much additional sprung mass can be safely carried per axle

Regulatory gross vehicle weight

Must not be exceeded for road legal compliance in Hong Kong [2]


Refined Motor Co.'s modular battery system is designed specifically to allow engineers to add or subtract individual battery units until the weight distribution sits within the original vehicle's tolerance. This is a key reason their conversions retain the driving character of the original car rather than producing a nose-heavy or tail-heavy result.



How Do Axial Flux Motors Change the Energy Budget?


Stepping back from the battery detail, a separate concern is how efficiently the installed energy is used. Motor efficiency directly affects real-world range: an inefficient motor consumes more of the available kWh per kilometre, shrinking the effective range even if the battery is well-sized.


Refined Motor Co. is moving to axial flux motors, the newest up-and-coming motor technology currently only found in supercars and ultra-luxury vehicles. Axial flux motors offer a significantly higher power-to-weight ratio and improved efficiency compared to conventional radial motors. For classic car modernization, this matters because:


  • A lighter, more compact motor leaves more of the weight budget available for battery capacity.

  • Higher motor efficiency means the installed kWh translates into more kilometres driven.

  • The compact form factor creates fewer packaging conflicts in tight vintage engine bays.


In practical terms, upgrading to axial flux technology extends the effective range achievable within the same battery size constraints, without requiring a larger or heavier pack.



What Does Road Legality Require from the Battery Installation?


Classic car EV conversion work in Hong Kong carries a regulatory dimension that shapes every hardware decision. Refined Motor Co. offers road-legal electric vehicle conversions in Hong Kong [2], which means its battery installations must comply with transport authority requirements, not just perform well on paper.


Key compliance factors that directly affect battery sizing and placement include:


  • High-voltage system safety standards governing cell chemistry, enclosure ratings, and thermal management.

  • Structural integrity requirements that prevent battery boxes from being mounted in positions that compromise crash protection.

  • Gross vehicle weight regulations that cap total vehicle mass, restricting how large a pack can be installed.

  • Wiring and protection standards for high-voltage systems, which require specific clearances and routing that consume physical space [2].


This regulatory layer means that the maximum possible battery capacity is not the target. The target is the maximum compliant battery capacity, a meaningfully different engineering brief.




Frequently Asked Questions


Q: Is 200-300 km WLTP realistic for a classic car conversion?


Yes. That range reflects what is achievable when the battery is sized to the space and weight constraints of a typical vintage platform. Compact or very lightweight vehicles may sit toward the lower end; larger platforms with more usable cavities can reach the upper end.


Q: Can I choose a larger battery for more range?


Only up to the point allowed by chassis space and vehicle weight limits. Installing a pack larger than the vehicle can safely carry creates handling, braking, and regulatory problems that outweigh any range benefit.


Q: Does a classic car EV conversion affect the vehicle's original character?


A well-executed conversion preserves the driving feel of the original car. Careful weight distribution during battery placement and the use of compact, efficient motors like axial flux units are key to maintaining the vehicle's balance and character.


Q: Is the conversion road legal in Hong Kong?


Refined Motor Co. offers road-legal electric vehicle conversions in Hong Kong



. All battery installations and powertrain components are engineered to comply with local transport authority requirements.


Q: What warranty is provided on the conversion?


Refined Motor Co. provides warranty coverage on its conversions, covering the electric drivetrain and battery system. Please contact the company directly for specific warranty terms and conditions.


Q: How long does the battery sizing and conversion process take?


Duration varies by vehicle complexity. Refined Motor Co.'s modular powertrain and battery system is specifically designed to reduce workshop time compared to bespoke one-off builds, but each vehicle requires its own dimensional assessment before work begins.


Q: Are high-voltage EV systems safe in converted classic cars?


High-voltage systems carry genuine risks that must be respected. All of Refined Motor Co.'s conversions are engineered and installed by qualified engineers following international high-voltage safety standards. DIY or unqualified high-voltage work is dangerous and should never be attempted.


About Refined Motor Co.


Refined Motor Co. is a road-legal electric vehicle conversion specialist in Hong Kong, founded by a team of engineers committed to modernizing classic and vintage vehicles through expert electrification. The company develops modular powertrain and battery systems in-house to solve the real dimensional and weight constraints of vintage platforms. Refined Motor serves individual owners, automotive dealers, and businesses seeking fleet electrification solutions, all backed by comprehensive warranty coverage.


Curious what battery capacity your classic car can accommodate, and what range that means for your driving needs? Refined Motor Co.'s engineering team assesses each vehicle individually and provides an honest, regulation-compliant answer before any work begins.




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