I had the old 510 system for years and it worked flawlessly. Then the batteries started to go. Rather than end up like ILVMYGT above and have it in a drawer, I contacted TST and explained my situation. They offered to take the 510 on trade for the upgraded 507 with replaceable batteries. I'm now going on four years with the 507 and couldn't be happier. They even through in a repeater so now I have two!....I should find it and ebay it...!.
Remember, tire monitors should do more than simply monitor PSI. The TST monitors pressure and temperature. So, if you have a caliper that sticks or some other 'issue' it'll show up before it catches on fire......Dennis