4 Days Out - S2-E9
Corrected entry: When Walt is building the battery and explains how it works to Jesse, he says that the cathode is the positive terminal. The cathode is always the negative electrode and the anode is always the positive electrode. Walt is a chemistry teacher who would know the difference. (00:37:15 - 00:38:30)
Correction: "Cathode" can be negative or positive (http://en.wikipedia.org/wiki/Cathode).