Why does the Xiaomi Focus Pen have poor battery endurance when it is charging on the Xiaomi Pad 7 Pro?

This is because the process of charging the Xiaomi Focus Pen requires the tablet to supply additional power, which adds to the overall system load. As a result, the tablet's battery can deplete more quickly, particularly if it is already at a lower charge level.
It is recommended to charge the tablet first to ensure it has sufficient battery when charging the smart pen. By following this practice, you'll help extend battery endurance and improve the charging experience for both the tablet and the Xiaomi Focus Pen.