The Nikon FG-20 has an electronic shutter, which will not work properly if no battery is inserted.

You can, with limited capabilities, still use the camera without a battery. Light metereing will of course not work, but the shutter speeds are also restricted to B and a mechanically controlled 1/90s indicated as 'M90' on the speed dial. Unfortunately, the camera will if no battery is inserted, use the 1/90s shutter speed if the dial is set to anything but B, so you have probably exposed all your images with a 1/90s shutter speed and not whatever you set the dial to. If that is still within the exposure latitude of whatever film you have used, chances are still great that you can get proper prints from the film.

This is IMHO a strange flaw in the otherwise quite meaningful user and operation designs presented by Nikon. It would have made much more sense if the shutter didn't release if the speed dial was set to an 'illegal' value. I did exactly the same mistake when I got my FG-20 and wanted to check if the camera worked before obtaining a battery. I first thought that the shutter was broken, since most of the pictures on the first films were incorrectly exposed, but then I realized that the camera needs a battery for the speed settings to work. With the FG-20 shutter being relatively quiet, it is also difficult to hear the mistakes, since all shutter speeds faster than 1/60s sound more or less the same. On many other cameras, the shutter sounds different on different speeds and such an audible feed-back can actually be quite useful to confirm that the camera is doing what you want it to do.