How can I preserve the battery level during use?

You can use the USB charger and the USB cable provided in the Tobii Pro Glasses 2 package to connect the Tobii Pro Glasses 2 Recording Unit Micro USB port (next to the LAN port) to charge the inserted battery.

Do not attempt to change the battery during a recording; the power provided via the USB cable is not sufficient to guarantee uninterrupted recording and might result in corrupted data.