The most common maintenance you will have to perform on the Ranger X1/X2 is tire changes. This helpful video from Kim Alexander shows how to swap out the rear tires and motors on the Ranger X1, this process is the same on the Ranger X2.
In case you can not power on the board, and can not determine whether it is the battery issue or the esc. Here is the video to show you how to use the diagnosis cable to find out.
For more general electric skateboard maintenance check out Daniel Kwan's video for how to take care of your board. Remember to regularly inspect all screws on your board and tighten them as necessary.