The SteelSeries Arctis 9 Wireless offers stable, completely reliable wireless connectivity in the 2.4 GHz radio and Bluetooth modes. The effective wireless range is around 10 meters, and the connection won't drop if you put a wall between yourself and the wireless dongle/Bluetooth source for a short amount of time. The headset is equipped with a Bluetooth 4.1 chip, which supports SBC and AAC Bluetooth codecs.
The headset connects to the wireless dongle by default, while Bluetooth is supposed to be activated manually if and when it's needed. Luckily, the SteelSeries Engine 3 software driver has a "Bluetooth Auto-Startup" toggle. If you activate it, Bluetooth will be turned on parallel to the 2.4 GHz radio connection when the headset is powered on.
Battery Life
As specified by SteelSeries, battery life of the Arctis 9 Wireless is 20 hours. I used the headset for three full cycles and was getting between 19,5 and 20 hours of usage out of it. That means most users won't have to charge it more than two or three times per week, which is very reasonable. The battery status can be monitored in the SteelSeries Engine 3 software, where you'll see a battery icon filled with an appropriate number of bars. To be honest, I'd be much happier with a percentile value. As mentioned earlier, the LED next to the power button also gives a rough idea of remaining battery life.
When the battery level becomes critical, you'll start hearing beeping inside the headphones. It can, of course, be used and charged at the same time. The headset also offers an auto-shutdown feature, which will turn it off when no sound input is detected for a set amount of time (5, 10, 30, 60, or 90 minutes).