In simplest terms back atcha' means, "Same to you." It's a positive connotation.
"Baby, you look so stylin'!" to which your baby says, "back atcha'.'"
by CaMaLibra February 14, 2014
Likewise; same to you.
When I congratulated her for a job well done, she replied, "backatcha!"
by Arizona Jaguar October 27, 2014