Here's a nice, slow verison on Appalachian dulcimer by sailplane enthusiast and YouTube user Tom McDonald, who says, "I recorded this at Ridge Soaring near Julian, PA on a day when I couldn't fly sailplanes due to the weather."
McDonald has a link to tab in DGD, the tuning in which he plays the song. (The song is usually written in G, and DGD is a wonderful "reverse Ionian" tuning well worth learning. But we play it in D.) It's available in "D for dulcimer" at http://everythingdulcimer.com/tab/battledul.pdf in tablature that includes fret numbers for both DAA and DAD. (Don't worry, if you want to experiment - they'll sound the same if you play either one, as long as everybody's tuned in D.) Either way, if you "play by number," you may want to get out a highlighter and mark the line of tablature you want to follow. If read music, of course, you can just play the notes!
Guitar chords - or "backup chords" - in G are available on line, for personal use only of course, at ...
Of course, you'll have to transpose it to D. You can do that by going to where it says "transpose" in the upper lefthand corner of the page and clicking down from G to D.
A couple of performances on YouTube
A string band in Michigan. More up to tempo, at least as I've heard it played. Fiddler Brad Battey joins Picks and Sticks on Aug. 7, 2010, at a wedding reception barn dance. Sherry Humecky on hammered dulcimer, Morgan Humecky on banjo, Bob Miller on bass, Alex Belhaj on guitar. Fiddler Brad Battey joins Picks and Sticks on August 7, 2010 at a wedding reception barn dance. Sherry Humecky on dulcimer, Morgan Humecky on banjo, Bob Miller on bass, Alex Belhaj on guitar. "Battle Cry" begins at 1:29.
Brass band - period instruments. The Federal City Brass Band's sunset concert atop Little Round Top at Gettysburg, November 2012. Brass bands and string bands of the 1800s often played the same music. Here's a better-than-average group of Civil War re-enactors playing on what look like period instruments.