You may notice that your phone's battery drains faster than usual while you are connected to a 5G network. This is a limitation of the current 5G networks, and will be improved as the networks expand.
At this time, the 5G networks are only used for data connections and are not yet capable of carrying phone calls and messages. Your phone will need to maintain a connection to the 3G or LTE network in addition to the 5G network so that phone calls, text messages, and data will be delivered consistently.
Because your phone is connected to multiple networks simultaneously, the battery will drain faster than one would typically expect, and the phone may get warmer than when solely on 3G or LTE. To make up for this, you can try using features that will optimize and improve your phone's overall performance. Navigate to Settings, and then search for and select Optimize battery usage to find these features.
As the 5G networks grow in capacity and capability, they will be able to handle more of your phone's functions with less battery drain.