I originally had a 1/2" corded dewalt hammer drill, it burnt up bits like a mofo no matter what brand of bit i used, even in low speed it was just too fast...which is the same thing i bet your experiencing with your cordless since my cordless hammer drill is too fast and just does'nt have the hammer action the bigger drills have.
I had 80 red heads i had to sink into sonotubes to hold up a boat load of steel posts supporting a large deck we were building so i bought a Bosche SDS demo hammer/drill and the past 5 yrs have bought nothing but the Bosche masonry bits for it and like the Hilti guys will attest to, there is simply nothing that compares to these drills for boring into anything cementious, everytime we use it i'm still blown away at how quickly it sinks the bits into even the oldest hardest concrete. I know that's not the answer your looking for, but the real answer is simple, your drill is just spinning way to fast, creating way to much heat and literally burning itself out and then eventually burning a flat tip on it LOL!! These Bosche SDS drills are very affordable, and are like any other "right tool for the job", even if it's only called upon a few times a year, those few times make it WELL worth the investment. PLUS as an added bonus there's a LARGE array or chipping/chiseling bits that you can call into action for a number of tasks...they make removing tile a breeze:clap: