Which of the following needs to be considered when retrofitting an electric-propulsion engine?

When retrofitting an electric propulsion engine, proper ventilation of batteries is crucial for safety and performance. Electric batteries can generate heat during operation and charging, and if this heat is not adequately dissipated, it can lead to overheating. Overheating not only reduces the efficiency and performance of the batteries but can also pose safety risks, including the potential for thermal runaway, which can be catastrophic. Therefore, ensuring that there is proper ventilation helps maintain optimal operating temperatures, thus extending the life of the batteries and improving overall system reliability.

It is also relevant to mention that considerations such as battery weight distribution, voltage increase, and cooling system expansion are important aspects of retrofitting but do not match the immediate priority of ensuring battery ventilation for safety and efficiency.