I have experience with this issue. You have pulled more amps than that battery can deliver.In my opinion those lipos are overated on the c rating. The 7700 will pull around 70 amps when geared hard. I did back to back tests with a 3600 poly rc 12 c and it preformed about the same as the one you have. They will usually shut down before they puff up though.If it's swelled it's done and i would not use it and dispose of it right away. A low turn brushless needs a higher capacity battery with a c rating that lets you pull 100 amps or more to be safe.