The SmartHub Gateway has built-in battery voltage monitoring.
When the Gateway is connected to your RV's 12V power system, it can monitor the voltage of your house battery. This works whether you're using the included 12V vehicle power adapter or the 12V direct-wire pigtail.
The kit also includes a separate RV Battery Voltage Sensor, which can be used to monitor another battery of interest, such as a chassis or auxiliary battery.