Energy storage upgrade
An energy storage upgrade can be used to upgrade a machine's internal power storage. Place one or more energy storage upgrades 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.
Besides this, it does not seem to have any effect on current machines, although it might be useable on batboxs, MFEs, and MFSUs in the future.