The optical devices receive their charge from magnetic connectors inside the charging case. The case needs to be connected to the USB-C charger that came with the unit. However, it’s important that the magnetic connectors in the charging case and underneath the optical devices are clean and free from debris in order to provide a good electrical connection. So if you experience any issues when charging please clean the magnetic connectors with a q-tip moistened in isopropanol. If that doesn’t help then just wiggle the device gently in its place and it should start charging.