To choose a right diode, you need to consider a repetitive peak reverse voltage and an average forward current of the diode rating.
Please refer to the following recommendations on how to determine them:
The repetitive peak reverse voltage should be at least twice the rated output voltage of PWR800L.
The average forward current should be at least four times the charging current.
For example, if the charging current is 10 A, select a diode with the average forward current rating of 40 A.A heat sink might be needed to dissipate the heat from a diode.