Di2 shifting is fully electronic. The electronic aspect of shifting allows for an easier, more seamless shifting transaction. In addition, Di2 shifting requires less maintenance than its manual counterpart, this is because the wires on the manual shifters over time have to be trimmed as they can stretch.
Per charge, you will get between 2,000km - 5,000km worth of range before the battery dies.
For more info on Di2 shifting, visit this link.
For troubleshooting Di2, visit this link.