EDIT - I am hearing from a friend that when you move the electrical gangbar it takes out the battery too, so also the standby instruments (an integrated EFIS).
From the AW139 Technical Notes
”Red Gang Bar moved backwards cuts off all aircraft electrical power sources at the same time. (Gen 1 & 2 and Battery Master switches are moved to OFF all together.)”
The Battery Master switch needs to be on to enable the Main and Aux to be connected to Main Bus 1 & 2.