MAVLink `BATTERY_STATUS` is decoded incorrectly

On the attached log file from a recent development build of ArduPilot, the `BATTERY_STATUS` message is decoded and displayed incorrectly in the log viewer. The file was captured with QGroundControl.

It shows the `id` field as a constant `NaN` and the `current_battery` field as a constant 65535. Other fields within that message and other messages seem to decode properly but I didn't search thoroughly for problems. All the messages look fine and the fields change how I expect when decoding with pymavlink. The `SYS_STATUS` messages also have the correct battery values.

[2024-12-07 12-44-46.zip](https://github.com/user-attachments/files/18049609/2024-12-07.12-44-46.zip)

Start by reproducing the issue with the attached 2024-12-07.12-44-46.zip log in the UAVLogViewer and inspect decoding of MAVLink BATTERY_STATUS fields. Compare the id and current_battery results with pymavlink and the SYS_STATUS values; done when those BATTERY_STATUS fields decode and display correctly without affecting other messages.

Written by the indexing model from the issue text.