The presented work identifies the dominating influencing factors in electric vehicle (EV) modelling on low-voltage distribution grids to establish guidance for reliable impact assessments of increasing EV penetration. Seven aspects are distinguished with respect to the modelling of the load of EVs that influence the flows and voltages in the grid. For each of these aspects sensitivity analyses are carried out by running power flow simulations in a Monte-Carlo fashion to account for the stochasticity in the model parameters. The impacts are analysed using a variety of metrics including transformer and line loadings. The highest sensitivities are observed for the number of vehicles in the grid, the used charger power rating and the modelling of driving patterns. The grid configuration as well as locally higher EV shares gain significance for line loading assessments. Car modelling and people's charging behaviour play minor roles.