rally 100 not always waking up and connecting

just bought a new set of rally rk 100. I have problems connecting them to my forerunner/edge. Sometimes they do, mostly they do'nt. Changed batteries, problem remains. Impossible to train with them as I never know if they are going to connect or not, let alone use them in racing.

garmin support just keeps suggesting the same thing, change batteries...

Any more useful ideas?

I hope this is not a standard issue