Victron products can use the information from the temperature measurement to charge the batteries depending on the temperature. This is particularly important for AGM and gel batteries, as otherwise they will be overcharged or not fully charged. There are a number of different sensors that you can use depending on your product. Some are included in the scope of delivery, others can be purchased separately. Check the data sheet to see whether the desired product (e.g. Multi, Quattro, BMV) includes the sensor in the scope of delivery.