Over the past 80 years, all of DC's Green Lanterns have proven that darkness cannot stand the light of their rings, which are some of the most powerful and iconic weapons of the DC Universe. While many different heroes have worn Green Lantern rings, the nature of the rings and the power batteries that fuel them have changed dramatically over the past several decades.
When Alan Scott, DC's first Green Lantern, stepped into the young DC Universe in a Martin Nodell story in All-Star Comics #16, what fans would come to know as a Green Lantern Power Battery was simply referred to as "The Green Lantern," and it spoke to Alan, explaining how to use its powers to fight evil.
As recently seen in Doomsday Clock, Scott's original lantern was made of metal, and Alan forged his ring out of the metal of the lantern itself. Wearing the ring allowed Alan to make his will a reality, giving him the ability to fly, phase through walls and project energy.
At the time, however, it wasn't clear what was inside the ring or its lantern. Alan simply referred to it as the emerald flame, but stories told decades later would eventually reveal that the ring, its lantern, and the energy inside of it were all part of a mystical object called the "Starheart."
Before they created the Green Lantern Corps, the Guardians of the Universe attempted to contain all of the magic in the universe into an orb, which they named "Starheart." This effort proved a failure, but the remains of that orb eventually found their way to earth and fell into Alan Scott's hands. Scott's metal ring and lantern are filled with mystic energy from across the universe that Alan controls through the power of his will.
All of this would change during the Silver Age when John Broome and Gil Kane created Hal Jordan and the Green Lantern Corps, forever transforming Green Lantern into a cosmic hero with a new origin for the character, his ring and the source of its power. Instead of being powered by magic; the Green Lanterns were now a technological marvel of incredible sophistication created by the mysterious Guardians of the Universe, who bestowed thousands of such rings upon worthy heroes from across the cosmos to create the Green Lantern Corps.
These rings were still controlled by the wearer's willpower, but the lantern they carried was now referred to as a Power Battery, and it was used to recharge the ring's energy every 24 hours while the Green Lanterns recited their famous sacred oath.
The rings and the power batteries are complex pieces of technology with many computerized components including an artificial intelligence with diagnostic and tactical capabilities. Both also appear to be made from some sort of crystal-like substance that can change shape and size to fit any alien appendage, no matter how large, small or strange. Though incredibly durable, the crystal material can be crushed and shattered, but it does not bend or crumple like metal.
Every Green Lantern's ring is charged using the energy from a power battery, and every power battery receives its energy remotely from the Central Power Battery on Oa. This massive structure is the source of every Green Lantern's power and serves as the focal point and reservoir of the grand might of the Guardians of the Universe as well.
The Central Power Battery itself is filled with an immense amount of amorphous green energy, which was eventually revealed to be the literal willpower of the DC Universe's emotional spectrum itself. The Central Power Battery absorbs the ambient emotional energy of willpower that radiates from individuals throughout the cosmos and stores it as literal energy within its crystalline walls. That energy is then shared and distributed wirelessly to the power batteries throughout the universe and kept there until a Green Lantern uses it to recharge their ring.
Though originally conceived as a creation of metal and magic controlled by will, the Green Lantern's iconic ring and power battery are now impossible scientific marvels that use a dependable system to collect the literal willpower of the universe and transfer that energy to the officers of the Green Lantern Corps as they combat the evils of the multiverse on its brightest days and blackest nights.