It charges through any of the four Expansion Card ports, currently through the USB-C card. Part of the reason we didn't use a fixed USB-C port for this is that

It charges through any of the four Expansion Card ports, currently through the USB-C card. Part of the reason we didn't use a fixed USB-C port for this is that the Expansion Card path allows for alternate power schemes in the future like magnetic attach, adapting to existing proprietary connectors, or even crazy things like POE.