I think you are right. 電池負極not接觸良好

This happenend to my car serveral times. I thgought it was the battery/alternator... a lot of possibilities. One day it would not start at all. I got it to a garage, the tech cleaned the neg post. It worked fine...I asked him to put in a new battery but I didn't have to... my guess is, he had the same problem. Putting a new battery fixed it because the process fixed the connection.