The lithium batteries in each valve stem last up to 10 years according to GM, but can have a much shorter life as some of us can attest too. If your sensors are 9+ years old, then bite the bullet so to speak and replace them when you put the new tires on. According to what I have read, and I don't know if this is true or not and maybe someone in the know will respond, but the batteries in the sensors are in the sleep mode until activated with either a magnet or the tire tool Tire Rack sells the tool for around $100+. C5s can use either the tool or the magnet, C6s require the tool to activate. Before I put my new Michelin tires on the 02, I will purchase the new sensors. As Tom said, the batteries in your OEM sensors cannot be replaced easily. His price list is accurate from what I have read. I read on the other forum that Corvette Guy Gal have all 4 sensors C5 and C6 for sale at $179 including the tire tool. When you purchase the sensors, make sure the gromet kit with the special nut is included for each sensor as you do not want to use the old ones off your current sensors. Make sure the tire shop knows about the TPS system on the corvette. There are horror stories on the forum about how tire shops ruin TPS systems on C4s, C5s, and C6s.
Barrett