Originally Posted by noideaatall
some are old, some I got already as a mobi and may not be converted. So it seems like it might be a good idea to convert them all again.
I'm not finging it a little tricky to use the command line. I'd like to convert everything from one directory and put the new compressed files in another directory - to see how much smaller they are and avoid the file names clashing.
any idea how to do this?
I don't know how to do it with Calibre, but you could unpack the files with mobiunpack.py, and then re-compile with KindleGen. This should get you the highest compression with fewest changes to the files.