The 714-140A-DVSR uses a dual sensing DVSR (710-140A). This system ensures that you will always have a fully charged reserve battery. When the switch is in position one, battery one becomes the sensing battery for the VSR. Battery two, which is in isolation, is charged through the VSR when the engine is running to ensure that it is always fully charged. When the switch is in position two, battery two becomes the sensing battery and battery one is charged through the VSR. The fact that there is always a fully charged battery in reserve is a huge safety benefit.