How do I refill a fire extinguisher in NYC. I went to the fire department and they do not refill them. I bought a new one but if the old one can be refilled, I would use it as a backup.
Look in the phone book under "Fire Extinguishers" or similar. In the NYC / Jersey area there should be hundreds of companies that service hand-held extinguishers - everything from hand-pump water cans to stuff that puts out exotic metal fires.
Note that if it is a very small domestic unit it may be cheaper to replace it.
The FD will check them, but not test or refill them. You do need a special place that does this for commercial units. Smaller household units cannot be refilled, they must be replaced.
Here is info from the NYC FD I found in about 2 seconds with Google: http://www.nyc.gov/html/fdny/html/safety/extinguisher/index.shtml They show links to dozens of fire extinguisher service companies.