1. Check the system parameter settings, "Forbid mains charging" is not selected in the main options, as shown in the picture below.
2.Check whether the fuse at the mains input terminal is intact, and whether the rectified DC voltage around 310V is correct.
3. After a few minutes of power-on, test whether the DC voltage at the output terminal of the charging transformer has risen.
The picture below shows the battery voltage DC53V when the mains charging transformer is not working just after starting up.
The picture below shows the battery terminal voltage rises to the charging voltage DC56V after the mains charging transformer starts working after a few minutes of starting up.