I had a 5 ml juice leak one day. I got juice on the balance connector. I didn't realize this till changing the battery and all was well till I left the mod sit for a few days and it drained the #3 cell down on the new battery also. It is OK now.
More on the story here:
DNA 200 Watt
And here:
Balance charging not working? - DNA 200 Early Adopters Forum
I'm going to do the same to the original battery, I'm quite sure there is nothing wrong with it.
BTW, my friend finally got his black and white Vapecig box from FT a couple of weeks ago and his battery has an XT 30 or XT 60 connector on the battery, I forgot which one. The door on his is screwed on .
Well I hope that fixes it permanently for you. Though it should have balanced it for you without you needing to run wires from your I4 to get cell 3 to match the others, It's supposed to be a balance charger after all. At any rate hopefully it stays balanced for you for the long run.