Energy storage upgrade
The Energy Storage Upgrade can be used to upgrade a machine's internal power storage. Place one or more into the four right-most slots to upgrade a machine. Each upgrade increases the storage capacity by 10,000 EU. Its main purpose is for use when a machine's energy consumption becomes too large for its internal storage to handle; this only happens when an extreme number of Overclocker Upgrades are present. It can also be useful for storing backup EU for when your energy generation stops functioning, but it is often more practical to craft more storage devices.
See: Crafting Guide