[BetterRed]

@phil_ga - try this

Set Preferences>Behavior->Preferred Input Format Order to whatever best suits, you probably only need to do this once and you've probably already done it.

Drag the books you want to convert from Windows Explorer into Calibre and leave the Explorer window open

1. Set Preferences>Behavior->Preferred Output Format = EPUB
2. Select the books you just dropped into Calibre as a group
3. Type 'C', and do what you need to do in the conversion dialogue, probably nothing
4. Click OK and wait for the group of books to convert
5. Drag the group of books from Calibre's centre panel (the list of books in the middle) into the folder you already have open in Explorer - this will copy the Preferred Output Format files - currently EPUB
6. Set Preferences>Behavior->Preferred Output Format = MOBI
7. Repeat steps 3 to 6 for the MOBI conversion
8. Do any necessary tidying up

BR