Do _Excel_Open once
Then the WorkBooks.
Don't need to switch Windows to get the values:
#include <Excel.au3>
Local $oExcel = _Excel_Open()
;Open Test1 Excel Workbook
Local $ofile = @ScriptDir & "\test1.xlsx"
Local $oWorkbook = _Excel_BookOpen($oExcel, $ofile)
;Open Test2 Excel Workbook
Local $mfile = @ScriptDir & "\test2.xlsx"
Local $mWorkbook = _Excel_BookOpen($oExcel, $mfile)
;Read Workbook data and display
Local $read1 = _Excel_RangeRead($oWorkbook, Default, "B2") ; Cell B1 in Test1 workbook contains the word Test1
Local $read2 = _Excel_RangeRead($mWorkbook, Default, "B2") ; Cell B1 in Test2 workbook contains the word Test2
MsgBox(0, 0, $read1 & @CR & $read2) ;Returns the correct values.