TARDIS power cell

TARDISes contained power cells. After the Doctor's TARDIS seemingly perished when it fell into Pete's World, the Tenth Doctor found a "insignificant little" power cell clinging onto life. By providing ten years' worth of his own life energy, enabling it to power the TARDIS back up within 24 hours. In the meantime, the Doctor used the power cell's energy to disintergrate a group of Cybermen. However, he could not do so repeatedly as the cell took four hours to recharge. (TV: Rise of the Cybermen)