Electric eels have 5000 -6000 cells called electrocytes. Each cell can generate a small amount of electricity ( 80 millivolts ) but by using their head and the tail to create a circuit around their prey the eel can create upto 500 volts of electricity.
In addition, the 500 volts can only be discharged momentarily in extreme circumstances. A much lower voltage is discharged continuously and acts pretty much like a radar, bouncing off the eels' surroundings thus enabling it to navigate through the murky waters it inhabits.