At the Ohio Historical Society there is the Kirchenberger Diary (he pretty much just records that he was captured in the battle). Their catalog also contains a summary of a German language diary (I would have to look up the name). The diary is missing but the summary suggests that it contained a reference to the battle.

The regimental history of the 9th Ohio Infantry has some references to members who also served in the 9th (including introduction by Tafel).

There was a letter written by an officer of the 106th which was referenced in several newspapers of the time (he is sometimes called Stalo and sometimes Spallo), but he did not witness the battle.

I have been working on a paper regarding Hartsville for a few years and would look forward to discussion with a fellow researcher.