Any search of black confederate will detail accounts of blacks serving in the confederate forces. A Walter E. Williams search will do the same.  Since many records were destroyed, during & after the war, exact #'s are hard to come by.
I didn't say blacks DIDN"T serve in combat units, but the MAJORITY served in rear areas, guarding supplies, frontier posts, rail bridges, etc.  
All the battles you specify occurred 1863 and later. Blacks didn't serve in the union army earlier. The black troops at Petersburg were "pulled" from the lead at the Crater due to "political considerations" of expected losses. They went in later, and were slaughtered, along with the white troops for running INTO the crater, instead of AROUND it! Much made of Confeds bayoneting black (and white) troops, but was undoubtedly in response to union troops bayoneting wounded and surrendering confederates earlier in the battle.