I removed the plastic sensors, the other week, but I could not get a grip on them to unscrew them, to replace the batteries! They have a retaining ring, which can be removed, and re-applied with the tab up, so that you can try to use it as a small wrench to unscrew the sensor from its watperproof cap (more on the waterproof cap, later). I also tried using a regular screwdriver to unscrew it, using the brass slot, in the middle of the sensor: this only managed to disfigure the brass slot!
I tried to use various pliers to grip the thin geared portion, to unscrew it from the cap: too low, too soft a plastic, to get a sufficient grip! I remembered that I had a Retainer Ring Pliers, which has small, metal cylinders, which would likely slot in between the teeth on the sensor. Had to go buy a new set of Retainer Ring Pliers, as I could not locate the old pair...
Success! The sensor has a rubber O-ring around it, which forms a water-tight seal, with the cap, which it is threaded into; the O-ring is translucent, semi-clear rubber, seen near the bottom of the sensor, on the right, below the 1225 numbers, near the bottom of the black plastic, in the photo, far right. It is this O-ring which created the tight seal, making it difficult to unscrew the sensor from its cap.
Also of note, is the Battery: CR1225. I only found BR1225 batteries (around $6 each, at Walgreen's; Wal-Mart did not have them). The difference between BR and CR batteries, is that the BR's have a voltage of a few tenth's lower, than the CR's. The BR's also have a slightly lower Amp-hour rating, which means they will not last as long as the CR's will. I recommend ordering the CR1225's off of Amazon, or some other retailer, to get the maximum lifespan out of the sensors.
One final, critical, note: check your TPMS sensor for which way the battery goes in! For mine, the +/positive battery pole is on top, away from the sensor, with the negative pole, the textured, un-labeled side of the battery, against the sensor housing. Be certain to put the batteries in with the proper polarity!
The TPMS system was worth the money: ~$60, off of e-Bay, two years ago? The battery change procedure was a little tricky, so I hope this helps others avoid the issues I encountered. Cheers!
Cheers!