Integration–Validation Trade-Offs in ICE-to-EV Retrofit Conversion: A Systematic Review and Readiness Framework for Sustainable Transport
This systematic review reveals that the stagnation of ICE-to-EV retrofit conversions stems not from a lack of evidence, but from a structurally disconnected evidence base where studies that broadly integrate vehicle systems fail to validate them deeply, resulting in a critical gap in technical and workforce readiness that prevents conversions from achieving certification or scale.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The world is trying to move away from cars that burn fossil fuels, shifting instead toward vehicles powered by electricity. This transition is essential for cleaning the air and reducing climate change. However, buying brand-new electric cars is expensive and requires a massive new network of charging stations, which many places do not yet have. A promising alternative is to take an old car with a gas engine and convert it into an electric one. This process, known as retrofitting, extends the life of existing vehicles and avoids the cost of manufacturing a new car from scratch. It sounds like a practical solution for a smoother transition, but for this idea to work safely on a large scale, the converted cars must be reliable, safe, and easy to fix.
A team of researchers set out to understand the current state of this conversion work. They did not build a car themselves; instead, they gathered and analyzed twenty-six scientific studies that had already been published about turning gas cars into electric ones. Their goal was to see if the research community was actually proving that these conversions are ready for the road, or if the evidence was missing critical pieces. They looked at two main things: how much of the car the researchers actually worked on, and how deeply they tested the safety and reliability of their work. They found a surprising and problematic pattern. The more of the car a study tried to fix, the less deeply they tested it. Conversely, the studies that tested safety very thoroughly often ignored the car's mechanical parts entirely.
The researchers organized their findings into a checklist of six different parts of a car that need attention during a conversion. These parts include the engine and wheels, the electric motor and its controls, the battery pack, the electrical wiring and charging systems, the physical frame and suspension, and the system that keeps the battery from getting too hot. They also looked at six levels of proof, ranging from simple design checks to full safety certification and finally, the readiness of mechanics to repair these new vehicles. When they mapped the twenty-six studies against this checklist, the picture became clear. The research was heavily concentrated on just a few areas. Most studies focused on whether the car could move and how far it could go. These performance tests appeared in nearly three-quarters of the papers.
However, the research was almost completely silent on other vital areas. Only two studies looked at the electrical safety systems that prevent shocks or fires. Just one study examined how to manage the heat of the battery, which is crucial for preventing dangerous failures. Perhaps most concerning was the complete absence of research on the people who would actually maintain these cars. No study connected the technical work of converting a car to the training needed for mechanics to service it later. In fact, twelve out of thirty-six possible combinations of car parts and safety checks were completely empty. No one had studied how to safely integrate the battery with the car's frame while also proving it was economically viable, or how to ensure the electrical wiring was safe while also checking the thermal management.
The study revealed a deep divide in the field. One group of researchers builds converted cars and tests how they drive, but they rarely check if the car is safe enough for public roads or if it makes financial sense over time. Another group writes about the costs and policies of electric vehicles, but they do not actually build or test any cars at all. These two groups are not talking to each other. Because of this split, the entire field of research is stuck at a very low level of readiness. Out of the twenty-six studies reviewed, only one managed to reach a level where the car was tested for both performance and basic safety. None of the studies reached a level where the car was certified for the road, could be serviced by a mechanic, or had a trained workforce ready to maintain it.
The researchers concluded that the problem is not a lack of good science. The studies they reviewed were well-written and followed rigorous methods. The problem is that the research is too narrow. Scientists are proving that a conversion works in a specific way, but they are not proving that the whole vehicle is safe and ready for the real world. The most critical missing piece is the human element. A car cannot be safe if there are no trained technicians to inspect it, repair it, or keep it running. The researchers argue that until the education system produces mechanics who understand both the old gas engines and the new electric systems, and until the research connects the technical work with the people who will do the work, these conversions cannot become a safe, large-scale solution. The path forward requires bridging the gap between engineering, safety testing, and vocational training, ensuring that every part of the car and every person involved in its life cycle is ready for the transition.
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