A few notes on the battery. I just this week bought an MG-1 locally off Craigslist in quite dirty condition, but was able to restore it and even get the meter working.
Use a letter opener to stretch the spring a bit, so the battery rig can touch the positive pole, which is the inside of the battery cover.
Tape two 1.5v LR44/357 button cells to the top of a 3v 123 battery, putting the tape around the sides so that both ends of the rig can make contact.
The battery goes in backwards than you might expect, with the flat bottom of the 123 going into the camera first, against the spring, and the taped LR44s sticking out until you put the cover on.
To activate the meter, press the shutter halfway down. Depending on overexposure or underexposure, one of the lights on the top should come on and a colored arrow light up at the top of the viewfinder.