The soul batteries are devices used by the Mursaat to store souls in order to power the Door of Komalie and prevent it from being opened. The soul batteries are powered by placing them above inscriptions on a bloodstone and killing on top of the bloodstone. Through the White Mantle, the Mursaat killed thousands of Chosen on top of the bloodstones. A single soul battery is capable of holding over half a dozen souls within it.
Six soul batteries are seen used on the bloodstone in Abaddon's Mouth and Hell's Precipice, and four over the bloodstone in Bloodstone Fen. Fifteen soul batteries in racks can be found in the eastern docks next to the one containing the soul of Leah Stone in Abaddon's Mouth, and there are two powering the Onyx Gate.