I read your post a few days ago and you jinxed me. I went out for a ride today and my 4iiii PM was dead.
I haven't kept track of how long I'm getting from the battery. But I seem to replace them more often during the part of the year when it's the coolest and I use the bike the least. Wish I'd known they were coming out with a rechargeable battery PM instead of the coin battery one. I've got a pile of coin batteries waiting to go to the battery recycling bin... where I've heard all they do is throw them away because battery recycling still cost more than mining the new raw materials.