biblatex2xml 4.16 reports biblatex “pages” and “pagetotal” fields as “unused tags” and omits them from MODS output, at least for some entry types, including @report.
For @report, these two are listed under “optional fields” in the biblatex manual, and actually I can see no harm in converting these fields, if present, for any of the biblatex entry types.
This issue is still present in 4.17.
AFAIS, "pages" is no longer an issue in 5.0, but "pagetotal" is still reported as "unused".
The information from the "pagetotal" field should be mapped to