Minecraft wiki entry for End_Crystal, associated text: Their primary purpose is to recharge the health of the ender dragon, who gains a charge from the nearest crystal within a cuboid extending 32 blocks from the dragon in all directions. The dragon is healed 1 each half-second. If multiple ender dragons are spawned, an end crystal can affect multiple dragons at the same time. The healing beam is neither obstructed nor is its power diminished by entities or blocks.