Electrification of transport in RES-based power system will support the decarbonisation of the transportsector. However, due to the increase in energy demand and the large peak effects of charging, the passiveintegration of electric cars is likely to undermine sustainability efforts. This study investigates three differentcharging strategies for electric vehicle in Europe offering various degrees of flexibility: passive charging,smart charging and vehicle-to-grid, and puts this flexibility in perspective with the flexibility offered byinterconnections. We use the Balmorel optimization tool to represent the short-term dispatch and long-terminvestment in the energy system and we contribute to the state-of-the-art in developing new methodologiesto represent home charging and battery degradation. Our results show how each step of increased chargingflexibility reduces system costs, affects energy mix, impacts spot prices and reduces CO2 emissions untilthe horizon 2050. We quantify how flexible charging and variable generation mutually support each other(����100TWh from wind and solar energy in 2050) and restrict the business case for stationary batteries, whereaspassive charging results in a substitution of wind by solar energy. The comparison of each charging schemewith and without interconnection expansion highlights the interplay between European countries in terms ofelectricity prices and CO2 emissions in the context of electrified transport. Although the best outcome isreached under the most flexible scenario at the EU level, the situation of the countries with the cheapest andmost decarbonised electricity mix is damaged, which calls for adapted coordination policy at the EU level.