OutBack Remote Temperature Sensor:
The RTS (Remote Temperature Sensor) ensures an OutBack system knows the precise battery temperature so that batteries can be recharged safely and efficiently. It is a necessary tool for proper battery charging. All OutBack products with integrated battery charging have a temperature compensation system built-in which benefits from the installation of the RTS (included with inverter/chargers). Systems with multiple OutBack products connected to one HUB4 or HUB10.3 require installation of only a single RTS.
More info:
https://documents.unboundsolar.com/media/UQ76aiN6-950010220-20Outback20RTS20-20Remote20Temp20Sensor20Installation.pdf?_ga=2.197937711.1262083624.1654649333-91488577.1654649333
