I am a beginner in MatLab Simulink and would like to measure the voltage across two electical nodes. I use Voltage Measurement to perform this task. However, i can not connect the positive and negative terminals of the Voltage Measurement to the nodes. There is a red circle appearing on the nodes. Anyone has similar problems and solve it? Thank you for your help in advance.
Your model is not built in simpowersystem environment so you can not use the voltage measurement block. The correct way to measure the voltage, is by using "voltage sensor" from Simscape>foundation library> Electrical> Electrical sensors. And then use "PS-Simulink Converter" to convert the physical signal to a simulink signal. And most importantly, use "Solver Configuration" to run your model as shown in the figure below.
The batteries nominal voltage is 12 V, so the scope shows a 24 V as expected,