Change battery and cable ends car acts like it.

Turn the head lights on so some current is trying to flow. Grab a test light and touch the ground clip to the negative battery post and the probe to the positive post. If it's not nice and bright, charge the battery at a slow rate for an hour. If it is bright, move the ground clip from the negative post to the cable clamp, (1/2" away). The light should still be bright. Move the probe from the positive post to its cable clamp. Keep moving the probe and clamp down the line until you find the spot where the light gets dim or goes out. That will be the point of the bad connection.