Convert from WINDOWS-1252 first to ISO8859?-1 with transliteration (so that smart-quotes are converted to ASCII quotes) then to UTF-8 (the new default encoding).
for i in*.bak do
iconv -f WINDOWS-1252-t ISO8859-1//TRANSLIT "$i"| iconv -f ISO8859-1-t UTF-8> $(basename"$i" .bak) done