Charles was born about 1845 in Michigan, the son of Benjamin (1810-1876) and Alzina or Alvina (1816-1868) and the brother of Harrison Soule, born about 1842 in Michigan. Both men enlisted in the 3rd Michigan Infantry. (See his full biography.)
Charles was taken prisoner on November 30, 1863 at Mine Run, Virginia, and sent to Andersonville, Georgia. Charles was struck down by dysentery and admitted to the prison hospital on March 24, 1865 with chronic diarrhea. He was exchanged on March 26, and admitted to McPherson hospital in Vicksburg, Mississippi from Camp Parole on April 7. Charles died in the hospital on April 20, 1865 and was buried in Vicksburg National Cemetery: section I, grave 7429.
Note, the cemetery is laid out on a series of stepped hills and many of the sections -- arranged by letter and then sequential grave number -- are not clearly marked if at all. Also, you will need to go to the USS Cairo Museum to ask about specific burials. They can provide you with maps -- also not very good -- and give you the general sense of where to look.