Firstly, congratulations on investing in safety equipment. Much like insurance, it's a 'cost' that doesn't always directly provide a return - but the day you need it, you will be happy you have it.
However, Extinguishers do need to be checked and maintained. So it's important to know when they will need checking and service them as necessary. If the Extinguisher is being used on a commercial vessel, then it's even more critical - as it likely impacts your insurance as well.
If you haven't already, check what the service date is on your Extinguisher and record a reminder down somewhere to have them replaced. If it's never been serviced, it's generally annually from the date of purchase (hence this email).
No, the Extinguisher won't suddenly stop working the moment it requires a service, but while the Extinguisher may still put out a fire, there's no guarantee – and do you want a flare to fail when you really need it?
Getting the Extinguisher Serviced
If you are not using the Extinguisher in a commercial situation, you could potentially just inspect the unit yourself. Checking the gauge is still in the green and turning the Extinguisher itself upside down and back ways up a couple of times - this second part can be particularly important for a powder Extinguisher on a boat - as the constant rocking and banging can settle and compact the powder over time.