I just got back from taking my one week old S90D from Massachusetts to Maine and back and discovered that my 11-year-old MA FastLane transponder (it predates the EZ-Pass transition) mounted in the black area of the windshield (no dots on the new windshield -- you get transparent or black) was read in NH, but not in Maine. Figuring it was the battery, I brought it to the Boston EZ-Pass office today and asked for a replacement. They tested it and said that it works fine and therefore will not replace it with a new interior transponder -- only with the big black license plate one. Knowing the problems people have had with license plate mounts and autopilot hardware (my model S has that), and not having a nosecone to hide it in (I have a refreshed design model S), I've decided to keep my FastLane transponder and try the rear parcel shelf mounting, but given the age of the transponder and its batteries, I'm skeptical it's going to work. I'll update when I've tried the new mounting with this ancient transponder, but a colleague here offered a good solution that I might consider if the parcel shelf mounting doesn't work: register with the Pennsylvania Turnpike to get one of their new interior EZ-Pass transponders. The claim is that they don't care if your plate is from out of state, and they would give me a more modern interior transponder. in the meantime, I'd love to hear more stories of EZ-Pass mounting successes from owners of the new design model Ss.