I haven't heard of the battle of Dunker Church either -- but I do know a little about the Dunkers!
The "Dunkers" or "Tunkers" was the nickname of "The Church of the Friends", a Pennsylvania Dutch Baptist group, somewhat related to the Mennonites, the Amish, and the Appalachian Primitive Baptists of modern-day snake-handling fame. Being early American Baptists explains their nickname: they were the first large group in their area to practice full immersion baptism, "dunking" converts. ("Tunker" is a slightly more derrogatory nickname variant of "dunker".)
Aside from being a pre-Revolutionary War Baptist group strongly settled in the mid-Atlantic Appalachians, they also had a claim to fame as the first and largest denomination to preach universal salvation as a doctrine (instead of only an occasional theological opinion). Their near-cousins the Primitive Baptists (of snake-handling fame) eventually picked up a split among their congregations along the same line, which is where you might have heard of "Heller" and "No-heller" churches. (Sometimes using the same church building, though using different doors to enter the sanctuary!)
The Friends are most famous nowadays, sort of, by being the Christian group behind the Heifer International charity. (They don't promote this, so aren't exactly 'famous' for it.
Also I'm not sure if the charity is still tied officially to the Friends.)
