1. Personally I think the gearing is too high. I ran 15&16/51 on my ERevo w/ emaxx tranny. A 20t is quite a step up form that.
2. That cell is def cooked, and most likely shot. Investigate a bit, but it looks like those 2 cells shorted, esp if this was sitting on a alu chassis.
Hard to tell more than this from the pics and info provided