mamba monster swolen capacitor

[nvtuning]

dear castle;

I was driving my flm savage yesterday and at some moment it started cogging so i checked the battery voltage's and they where 3.76volt per cell
so i tryed again but it didn't want to move anymore when i use only one battery (2 cells) it works great but with two packs (4cells) again it does nothing.
But after opening up the case i saw this this can't be good what should i do.



the setup i'm running is:
mamba monster (ofcourse)
the 2650kv motor from castle (the one that came with the esc)
and 2x 2cells lipo's 5400mAh (in series so it becomes one 4cells)

already thanks

greets nvt