If your stopped on the water by any of the authorities, one of the items that can be checked and required along with pleasure craft licence, life jackets etc is, is there a fire extinguisher on board, is it charged, is it the right size and type for the craft, the proper number of and is it 10 years or less in age. The rules that govern extinguishers on board are, length of the craft, is it an inboard engine, does it have a fixed fuel tank and if there are any fuel burning appliances as in cook/oven stove, heater or refrigerator.
I don't throw away my expired extinguisher. I maintain it as mentioned above as long as it remains charged, keep it stored on board in a handy accessible location, just in case it might be needed. The good ones, as I need two, are in the proper locations as required. I'm also only require to have the 5 lb. B.C type but opted to carry 10 lb ABC's