One more thing I remembered about fire extinguishers.... concerning them being stored in vehicles.
The Fire Department here dismounts them periodically to beat them with a rubber mallet while holding them upside down/sideways. They do this to "dislodge" the powder that settles at the bottom....... all of the vibration etc. caused by being in a vehicle really settles/concentrates the powder at the bottom. So much so that it's problematic.
I wonder if the same should be done for a smaller unit stored in a "regular" vehicle?.... their trucks rattle like crazy just idling.