The Central Power Battery is the reservoir of power for the emotional spectrum of willpower, and channels the energy used to empower the Green Lantern Corps. All of the green energy housed within a Green Lantern ring comes from a smaller battery, which in turn, functions as a conduit to the Central Power Battery on Oa.
The Central Power Battery has been destroyed twice before. The first time, everyone was left powerless except for Hal Jordan. The second time Hal Jordan himself, controlled by Parallax, destroyed the Central Power Battery and killed many Green Lanterns and even all but one Guardian. Ganthet, the last remaining Guardian, fled to Earth where he gave Kyle Rayner the last Green Lantern Ring.
For years Green Lanterns had no effect against the color yellow. When Hal Jordan was resurrected it was revealed to be the result of Parallax having been long ago sealed inside the Central Power Battery. Parallax feeds off of fear and yellow is the color that represents fear in the emotional spectrum. If a Green Lantern can overcome their personal fear than they can overcome the yellow impurity.
The Central Power Battery comes under attack many times during the events of the Sinestro Corps War and Blackest Night. During the War of the Green Lanterns, Parallax is placed back inside the Central Power Battery, allowing him to control all Green Lanterns currently wearing their ring.
Each of the new Corps representing the emotional spectrum has their own Central Power Battery in some capacity.