Questions about Popp Z-Rain

You need a Z-Wave gateway (e.g. a Fibaro Homecenter or a Raspberry solution). With this, the device is primarily connected in your Smarthome. Depending on the solution there, you also have remote access (I, for example, have integrated it into Homeassistant and can access this remotely and thus also see the measured values from the Popp Z-Rain).

Yes, according to the manufacturer's page with two standard AAA batteries.