Does a Nikon FG work without batteries?

I've just gotten my dads nikon FG out of the attic and hooked it up with some film and batteries. I set it up all ready for the first photo, but wasn't ready to shoot anything yet so I took the batteries out. I was fiddling around looking through a lens while the batteries were out and pressed the caption button (unaware of correct term for that) and it took a photo! I was unaware this could happen. Does it need batteries at all?

Shutter release.

While the FG has an electromagnetic release and quartz-timed - battery dependent - shutter, Nikon often made the X-synch speed (around 1/90th) mechanical. It was a back-up if the battery failed.

If you intended to use flash, you would've set this speed deliberately, or maybe the camera was left on this speed.

The battery is for the hot shoe.

AVDADDY, do you just make this stuff up?!

As Andrew points, out the FG features an electronically timed shutter. Instead of containing gears and levers like an old clock that determine how long 1/60th or 1/1000th of a second are, a microcomputer does this. And as you can imagine, computers need electricity to run. So no, the FG or any electronically timed camera, can't FULLY work without batteries. Nearly all cameras with an automatic shutter mode can't work without batteries. Also, if you have the camera set to "A" or aperture priority mode, the camera needs the light meter to function in order to determine how much light is in a scene and therefore what shutter speed to select.

However, also, as Andrew points out, many electronically timed shutters feature at least one mechanical shutter speed, in addition to bulb to allow for very very basic operation if the batteries were to fail or other reasons. On the FG, 1/90th is the mechanical speed and it's signified by the letter "M" beside the 90 on the shutter speed dial.

100% mechanical cameras like the Nikon FM only require a battery for the light meter but can function perfectly fine without them.

Another note, the "caption button" as you're calling it for some reason is properly named the Shutter Release as you can find in the manual for the FG as well as the above information:

http://butkus.org/chinon/nikon/nikon_fg/nikon_fg.htm

Finally, you are probably not finished preparing your FG to shoot again. Unless it has been serviced in the last 10 years or so, the foam light seals in this camera are rotten and need to be replaced before they damage the viewfinder and cause light leaks to occur on your photos. You can learn to replace the seals yourself or hand the camera over to a repair shop to do so for about $30 in many cases.

If you need more advice on this, ask another question here or email me at JohnnyMartyr@Hotmail.com

Happy shooting!

Does a Nikon FG have to have film in it in order to determine if it is working? I replaced the batteries but still nothing.