I'd try the battery first. Mine glitches out all the time, but I think it's only when my jersey flaps in the wind against the sending unit.

The "Deluxe Soft Strap" is the one I have which absolutely sucks, and I've seen no response from Garmin. Some people blame the contacts being too dry, recommending conductivity gel, some say water. Some also blame static electricity for the glitches.

I've kept mine wet, wrapped the sending unit in anti-static sheets, wrapped and pinned a sock around it, worn it upside down, on my back, etc. Nothing works.

I personally think it is from my jersey flapping against the sending unit in the wind, so I can either unzip my jersey to my stomach, or never go to the drops. Either "solution" sucks. I also tried using the Garmin sending unit on a Polar Wearlink+ and that was even worse (the contacts dried out more readily).