Mega Energy is essentially an upgrade to regular Energy, with slight differences in appearance and properties. Mega Energy is a slightly darker, larger variant of Energy which can restore all of Glitch's battery life, regardless of how much Energy you've lost.
Mega Energy can be found in various places later in the game, from Shady and Mr. Pockets for washers, and can be found simply lying on the ground in relatively hidden or open locations. They cannot be dropped from any enemy in the game.