The shield battery is a protoss support structure. Its core contains a khaydarin crystal that absorbs and stores local psionic energy. The stored psi is transferred to protoss units via the energy spokes, allowing plasma shields to be recharged rapidly. While the battery has a limited energy capacity, it will steadily recharge itself over time.
The shield battery retains its role in StarCraft II as a structure that restores protoss shields. It was added into multiplayer in Patch 4.0.
In multiplayer, the shield battery restores shields of a single friendly unit within 6 range. Shields restore at 50.4 shields per second, drains 1 energy for every 3 shields restored. This ability is autocast on friendly units and photon cannons.
The shield battery appears in the campaign of Legacy of the Void as a basic building requiring a nexus. Their shield recharge can be set to autocast, which makes them considerably more useful. However, they only restore the shields of defensive turrets when set to autocast, not other buildings.
The following section contains information from a previous version of StarCraft II which is no longer valid.
It appears that the shield battery was once part of the StarCraft II game engine prior to the game's release. In 2008, Karune stated that the shield battery would not be available in multiplayer games. It did not appear in the Wings of Liberty product. In September 2017, Blizzard stated that they were looking into bringing the campaign shield battery into Legacy of the Void multiplayer, as a 75 mineral structure that can recover allied shields even as they are in combat. The addition of the shield battery was tested in the testing matchmaker. At BlizzCon 2017, it was announced that the shield battery would become a standard structure in multiplayer matches, and it was added in Patch 4.0.