Hello, That's right, the outdoor station (wind direction and speed, temperature, humidity, solar and UV index) have a solar cell that is sufficient for the necessary power supply during the day. At night and when the solar cell is covered with snow, it is mandatory to insert AA batteries in the compartment provided on the outstation. The transmitter sends a data packet to the display unit inside every 16 seconds. And this does not work without electricity 😊. I don't know how long the batteries will last, I've only had the station since November and have never had to change the batteries.