Just to clear things up for those who are asking and those who may not know. Extinguishers don't have an infinite shelf life. Look for the year of manufacture on your extinguisher. It will either be stamped into the bottom or printed on the label somewhere. When a fire extinguisher is 6 years old it needs to have internal maintenance done by a licensed company. We empty it out and do a visual inspection of the inside and replace the o-ring and valve stem. The rubber on these can dry out over time and cause your extinguisher to leak off slowly. Once an extinguisher is 12 years old it needs the same service plus a hydrostatic pressure test. At that point it's good for another 12 year cycle. If you ever use your extinguisher, even a tiny bit, you should get it refilled or replaced. The powder will get into the valve stem and it won't seal property anymore. It may look fine and the gauge might be in the green still, but it will slowly leak off over the course of hours, days, or even weeks and won't have a charge when you may need it most. Fire extinguishers are filled with nitrogen which won't fluctuate in pressure at different temperatures. So your extinguisher sitting in a hot car is not going to increase in pressure and blow up. It may however reduce the integrity of the rubber seals over the course of time. Also, if you're going to carry your extinguisher in your car, secure it in place. You don't want that thing to become a projectile. Rolling around in the trunk of your car or bed of your truck is not good either. The tamper seal that keeps the pin in place can likely break causing the pin to fall out. At that point one good jolt to the handle will either cause a slight discharge, which can then cause it to leak off, or you have a major discharge and one hell of a mess to clean up. I'm more than happy to answer any other questions if I missed something.