Just out of interest, the last warranty replacements, did they replace the TX or the battery? I ask because when they replace the battery they replace the outside shell too.
The first time I had batteries replaced the service center didn't allow the TX to sit for long enough without the battery and reset, so I was given an incorrect battery life. Suunto have exchanged my transmitters twice, unfortunately when they went back they were sent without the batteries, so they couldn't tell if the batteries were at fault or not. I had maybe 3 visits to my dealer this year. They seem to all be okay now.
You should record all the S/n of the units and send the issue to them, in my experience if they replace a unit your 2 year warranty starts over from that date on those TX
Annoyingly my wife has one of the early TX, its the only one that hasn't had a battery issue nor been replaced.