> Using dual-port modules, the system recognizes that, say, one smartphone battery in the vehicle is at 5 percent of capacity and a second phone is at 75 percent. The programming module gives the former device 100W and the latter 25W.
Here's an example capture of an exchange between my MacBook Pro and iPad: https://imgur.com/a/8rZlN9X
The iPad responds to Get_Battery_Cap with Battery_Capabilities, which reports the total capacity in Wh:
USB Vendor ID: 0x05AC Product ID: 0x0000 Design capacity: 280 Last full-charge capacity: 280 Battery reference: valid
And then when the MBP asks for battery status, the iPad returns a Battery_Status message:
Battery is present. Present capacity: 14.2Wh Charging state: charging.
Later on, as the charging continues, the iPad will issue an Alert message:
Reported alerts: Battery status changed. Affected batteries: Fixed battery slots: 1
And then the MBP will send a Get_Battery_Status again, and so on. (Example capture here: https://imgur.com/a/TI5maV0
What's really cool is that this exchange happens both ways—the iPad also sends a Get_Battery_Cap message to the MBP, because it is also capable of acting as a source, and, if the laptop's battery drops sufficiently low, the source/sink roles may swap (using a DR_Swap message) so that the iPad ends up charging the MBP!