Electric truck charging may lead to new future challenges in the power grid, which are difficult to assess from today's perspective. One way to deal with the lack of measurement data and empirical values is the generation of synthetic charging profiles. This paper presents an approach to consider charging profiles of electric trucks in future grid planning. For the charging profile generation, real journey data of conventional trucks are combined with vehicle parameters of battery-electric trucks and legal regulations on breaks and rest periods. This results in time series of the truck's location and state of charge for an entire year. The time series can be converted into charging profiles by specifying fixed charging locations and charging power. The applicability of the presented methodology is tested using a truck fleet based on German mobility data. This allows not only the determination of the yearly energy and power requirements of electric trucks with different weights and application classes, but also the estimation of changing mobility behavior when switching from conventional to electric drives. The presented approach is therefore of great interest to both grid planners and fleet operators.