How to use Voltage Measurement in Matlab Simulink?
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,