I have a Nikon FG 20, which I brought on a trip to take pictures. I used Fujifilm Fujicolor 200 film, and I've already used all 36 shots. Recently, I found out that my camera has a battery compartment. By any chance, was I able to actually take any pictures? Or would I just waste my money developing a blank roll?
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.
It depends on the specific camera. The Pentax K1000, for example, only requires the battery for metering, but everything else is mechanical. On your camera, shutter timing is electronic and requires a battery — but according to the manual there is a special setting
M90 which provides a 1/90th of a second shutter speed which is all mechanical and can be used without the battery. (In fact, the manual even suggests setting to this speed when the camera is not in use to prevent battery drain!)
Apparently the camera falls back to this manual shutter if there is no battery. This is a rather poor user interface choice, since generally doing nothing is preferable to doing something unexpected. But, the good news is that if correct exposure was at least close to that being right, and it might have been in many situations, film is pretty forgiving and you might still get usable results. I think it's worth having the film developed to find out.
If the film advanced and you heard the shutter fire, there's a good chance you captured something. Based on info mattdm provides, the film may be under or over exposed, depending on whether photos were taken indoors or out, because of the fixed shutter speed.
You can try using the camera while examining the shutter to see what happens. Consider taking the camera and film to a local lab, explain what happened, and ask what they think.
Even if the film was exposed, if you feel the photos you took may not be worth keeping, you might not want to bother developing it. You might also consider purchasing a development kit, if you're interested in experimenting with home development.