Battery won't hold charge on Mitsubishi Galant

Sounds like you have a loose or dirty connection on the negative cable. An easy way to verify that is to turn on the head lights to be sure something is trying to draw current, then use a test light to check where the voltage is lost.

Start with the ground clip right on the battery's negative post, not the cable clamp, and the probe on the positive post. The light should be bright. Move the probe a half inch from the positive post to the cable clamp. If the light is dim or out, that connection is bad. If it's still bright, move the ground clip from the negative post to that cable clamp. If the light is out now, clean and tighten that connection.

If necessary, keep moving the clip and probe further along the wires until you find the spot where the light goes out. Follow the small negative wire to the body. The positive wire usually bolts to the under-hood fuse box.