Circulating a lot of energy, electric cars batteries heat up naturally, like the battery in your phone after intensive use. Without any temperature or voltage control, the risk of fire exists. To function correctly, lithium-ion batteries must maintain their temperature between 20 and 35 ° and must not exceed 40 °.
However, this monitoring and the regulation that follows if necessary cannot be done without a minimum of energy so that the sensors which watch the cells operate and collect the data, and that the control system (Battery Management System, or BMS) can make the right decisions. Concretely, the accumulator always retains at least 4 or 5% of energy, but they are no longer intended to move the car forward, which stops.