Complex sentence: In a fight that cut off Unit 01's main power source and drained it's backup power, Zeruel nearly destroyed Unit 01, slicing off its left arm in the process, but before it could land the final blow, Unit 01 went berserk.
Split into simpler sentences: In a fight that cut off Unit 01's main power source and drained its backup power, Zeruel nearly destroyed Unit 01, slicing off its left arm in the process. Before it could land the final blow, Unit 01 went berserk.