TARDIS power cell
From Tardis Wiki, the free Doctor Who reference
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. (TV: Rise of the Cybermen)
In the meantime, the Doctor used the power cell's energy to disintergrate a group of Cybermen when they refused his surrender. However, he could not do so repeatedly as the cell took four hours to recharge. (TV: The Age of Steel)
