My wife and I have used 2 FGs for the better part of a decade now. There is a secret to save the battery! Look at the shutter speed dial. The "A", "P", and numbered settings are all electronically controlled. The "M90" and "B" settings are fully mechanical, though they still close the circuit to the hot shoe. Any and every time that you are not using the camera, rotate the shutter speed dial to either "M90" or "B". This ensures that the battery will not drain, even if the shutter spring is weak or something slightly presses the shutter down. My batteries last for 2 or 3 years shooting around 25 rolls a year.

In short, always leave the shutter speed dial on the mechanical settings and the electronics will not drain. Leaving the dial anywhere else while the camera is in storage can drain the battery.