What an electric car conversion kit does—and what it doesn't

An electric car conversion kit replaces your petrol or diesel engine with an electric motor, battery pack, and charging system. It does not turn your car into a new vehicle; it retrofits the drivetrain into the shell you already own. The kit includes the motor, high-voltage battery, power electronics (the controller that manages power flow), and wiring harnesses. What it does not include—and what you will have to source, fabricate, or pay a shop to handle—is the structural work, cooling systems, weight distribution changes, and integration with your existing brakes, steering, and suspension.

The appeal is straightforward: you keep a car you know, avoid the cost of a new electric vehicle, and reduce running costs. The reality is more complicated. Conversion kits range from bolt-on systems for straightforward vehicles (usually older, lighter cars) to full custom engineering jobs. A kit that works on a 1970s Volkswagen Beetle will not work on a 2010 sedan. The motor size, battery capacity, and mounting points are specific to each conversion. You cannot buy a universal kit and expect it to fit your car without significant modification.

Key Takeaways

  • Conversion kits replace the engine and fuel system with an electric motor and battery, but you or a shop must handle structural changes, cooling, and integration with existing systems.
  • Kit cost ranges widely depending on motor size and battery capacity, but labour and fabrication work often exceed the kit price itself.
  • Your car's weight, structural integrity, and braking system must be assessed before conversion, because electric motors and batteries are heavy and change how the car handles.
  • Insurance, registration, and roadworthiness testing vary by region and often require inspection by a certified engineer or vehicle authority.
  • A converted car will not have the range, charging infrastructure support, or warranty coverage of a factory-built electric vehicle.

What's actually inside a conversion kit

The core components are the electric motor, the battery pack, and the power management system. The motor is usually a DC brushless motor or an AC induction motor rated between 20 and 100 kilowatts, depending on the kit and your intended use. A 40 kW motor is roughly equivalent to 54 horsepower—adequate for city driving but not highway acceleration. A 100 kW motor approaches 134 horsepower and is more suitable for performance or highway use.

The battery pack is the heaviest and most expensive part. Most kits use lithium iron phosphate (LiFePO₄) cells arranged in modules. A typical conversion kit includes 40 to 100 kilowatt-hours of capacity. That sounds large, but it translates to a range of 80 to 200 miles depending on the motor size, vehicle weight, and driving conditions. A factory electric car with the same battery capacity will often achieve longer range because the entire vehicle was engineered around that battery from the start.

The power electronics—the controller, onboard charger, and DC-to-DC converter—manage how electricity flows from the battery to the motor and to the car's 12-volt systems (lights, wipers, instruments). These components must be sized to match the motor and battery. A mismatch means the system will not perform as intended or may fail under load.

The hidden costs: labour, fabrication, and engineering

A conversion kit itself typically costs £8,000 to £25,000 depending on motor size and battery capacity. That is the starting point, not the total. Labour to install the kit, fabricate motor mounts, relocate fuel tanks or modify the chassis, and integrate the electrical system usually runs £5,000 to £20,000 or more. A shop experienced in conversions will charge by the hour, and the work is not fast—expect 200 to 400 hours for a complete job.

You will also need to address cooling. Electric motors generate heat, and the battery pack must be kept within a safe temperature range. Most kits include a basic cooling system, but integrating it into your car's existing cooling loops or adding a separate system adds time and cost. If your car has air conditioning, you may need to replace the compressor with an electric version, another £2,000 to £4,000.

Structural work is often the biggest surprise. The battery pack is heavy—200 to 400 kilograms depending on capacity. Mounting it safely requires reinforcement of the chassis or floor. If the kit is designed for a specific car model, the mounts may bolt in place. If you are converting an older or unusual vehicle, a fabricator will need to design and weld custom brackets. This work must be done correctly; a loose battery pack in a crash is a serious safety hazard.

How the conversion affects your car's handling and safety

An electric motor and battery pack change your car's weight distribution and centre of gravity. Most conversions place the battery low in the chassis (under the floor or in the rear) to improve handling, but this raises the car's overall weight. A light car might gain 300 to 500 kilograms. That extra mass affects acceleration, braking distance, and how the suspension responds.

Your braking system must be reassessed. A heavier car needs more braking force to stop in the same distance. Many conversions retain the original hydraulic brakes but upgrade the pads and fluid to handle the extra weight. Some kits include regenerative braking, which captures energy when you slow down and feeds it back to the battery. Regenerative braking reduces wear on the friction brakes but does not eliminate the need for them, and it requires a compatible motor controller.

Crash safety is a real concern. The battery pack is a large, heavy object mounted in or under the car. In a side-impact or rear-impact collision, the battery must not rupture or shift. A professional conversion shop will have the battery enclosure tested or certified to withstand impact. A DIY conversion or a shop without proper engineering may not. Before you commit to a conversion, ask the shop for documentation of how the battery is protected and whether it has been tested.

Registration, insurance, and roadworthiness testing

A converted car is not automatically legal to drive on public roads. In the UK, a converted vehicle must pass an Individual Vehicle Approval (IVA) test or a Single Vehicle Approval (SVA) test, depending on when the original car was built and the extent of the modifications. The test is carried out by a designated testing station and covers emissions (zero for electric), noise, structural integrity, electrical safety, and braking performance. The cost of testing ranges from £500 to £2,000.

Your vehicle registration document (V5C) must be updated to reflect the change in fuel type and power source. You will need to notify the DVLA and provide evidence of the conversion work and any approval testing. The process varies by region; some areas are more familiar with conversions and process applications faster than others.

Insurance is more difficult. Many standard car insurers will not cover a converted vehicle because it falls outside their underwriting guidelines. You will need to find an insurer willing to cover modified vehicles, and they will likely require proof of the conversion work, engineering documentation, and approval testing. Insurance premiums for converted cars are often higher than for equivalent factory-built electric vehicles because the risk profile is less certain.

Range, charging, and real-world performance

A converted car's range depends on battery capacity, motor efficiency, driving style, and terrain. A 60 kWh battery in a light car might deliver 150 miles of range in city driving and 100 miles on the motorway. The same battery in a heavier car will deliver less. Cold weather reduces range by 20 to 40 percent because the battery loses efficiency and the motor works harder.

Charging speed depends on the onboard charger included in the kit. Most kits come with a 7 kW charger, which adds about 30 miles of range per hour on a standard 32-amp home circuit. A faster 11 kW or 22 kW charger requires a dedicated circuit and adds 50 to 100 miles per hour. Public rapid chargers (50 kW and above) are not compatible with most conversion kits unless the kit includes a compatible DC charging port—an expensive addition.

Performance is honest but modest. A 40 kW motor will accelerate a light car from 0 to 60 mph in 12 to 15 seconds. A 100 kW motor in the same car will do it in 6 to 8 seconds. These figures are respectable but not thrilling, and they assume a fresh battery. As the battery ages and its capacity declines, acceleration and range both drop. A factory electric car with the same motor size will often outperform a conversion because the entire powertrain was optimised together.

When a conversion makes sense—and when it doesn't

A conversion is most practical for older, straightforward vehicles with strong structural integrity and no complex electronics. A 1970s or 1980s car with a solid frame, straightforward steering and braking, and no computer systems is a good candidate. The car is already paid for, so the conversion cost is an upgrade rather than a replacement purchase. You have an emotional attachment to the vehicle and want to keep it on the road.

A conversion is less practical if you need long range, fast charging, or a warranty. A factory electric car with a 60 kWh battery will cost £25,000 to £40,000 new (or £15,000 to £25,000 used) and comes with an 8-year battery warranty, roadside information, and access to public charging networks. A conversion of similar capacity will cost £15,000 to £30,000 in parts and labour, requires ongoing maintenance and repairs you must source yourself, and offers no warranty. If you drive more than 150 miles per day regularly, a conversion is not suitable.

A conversion is also not practical if you cannot commit to the engineering and testing process. A shop will handle the work, but you must be involved in decisions about motor size, battery capacity, cooling, and safety systems. You must also be prepared for delays, unexpected costs, and the possibility that the finished car will not perform exactly as you hoped. If you want a car that straightforward works, buy a factory electric vehicle.

Frequently Asked Questions

Can I convert any car to electric?

Technically, yes, but practically, no. Older, lighter, simpler cars are easier and cheaper to convert. Modern cars with complex electronics, integrated engine management, and advanced safety systems are difficult to convert because the conversion must interface with or replace these systems. A car with structural rust or damage is not a good candidate because the conversion adds weight and stress to the frame.

How long does a conversion take?

A straightforward conversion of a straightforward, well-documented vehicle typically takes 200 to 400 hours of labour. A shop working 40 hours per week will need 5 to 10 weeks, plus time for parts procurement and any unexpected issues. Custom fabrication or engineering work can extend this to 3 to 6 months. Plan for delays; many shops have long waiting lists.

Will my converted car be as reliable as a factory electric car?

Reliability depends on the quality of the conversion work and the components used. A conversion done by an experienced shop using quality parts can be reliable, but you will not have the same warranty or support infrastructure as a factory vehicle. When something fails, you must find a technician familiar with your specific conversion, which may be difficult. Factory electric cars have established service networks and known failure modes.

Can I sell a converted car?

Yes, but the market is small. Buyers are typically enthusiasts or people specifically looking for a converted vehicle. The resale value is usually lower than a factory electric car of equivalent age and condition because of the uncertainty around long-term reliability and the difficulty of insuring and servicing the vehicle. Expect to recover 40 to 60 percent of your total investment if you sell within 5 years.

What happens if the battery fails after the conversion is complete?

Battery replacement is expensive—typically £8,000 to £15,000 depending on capacity. Most conversion kits do not come with a warranty on the battery beyond the manufacturer's standard (usually 5 to 8 years or a certain number of charge cycles). After that period, battery replacement is your responsibility. Budget for this cost when deciding whether a conversion is worth the investment.