Each Battery Voltage sensor measures a single DC Voltage. Up to 10 Battery Voltage sensors can be added to a single RV Whisper® monitor station (sold separately). Motorized RVs typically use two sensors: one for monitoring the house batteries and one for monitoring the starting batteries. With the Battery Voltage Sensor included, you can: * Monitor your house batteries' and starting batteries' state of charge * Add up to 10 battery voltage sensors to your RV Whisper Monitoring Station