Massive integration of electric vehicles (EV) into power systems will pose significant challenges, in particular to distribution systems. Additional peak demand by EV charging can induce congestion or voltage issues, which would require costly infrastructure investments. However, these impacts can be reduced by using smart charging mechanisms. The impacts of EV charging and the efficacy of smart charging algorithms will depend on user behavior (namely travel and charging patterns). This study analyses the impact of non-systematic EV charging on base load, at the HV/MV substation level, and on smart charging potential. Case studies on realistic substations, based on real travel and grid data from France, exemplify the results.