Abstract: An end-of-discharge voltage correction section subtracts, from an end-of-discharge open voltage, the product I×RO of a discharge current I of a block and an ohmic resistance RO of the block and the product ITD×RP of a discharge current ITD obtained by performing a time delay process on the discharge current and a polarization resistance RP of the block. Then, a resulting value is set as an end-of-discharge voltage VL. The ohmic resistance RO is increased as an equivalent cycle count CY increases, and is increased as a healthy parallel number NPH decreases. An increment ?CY of the equivalent cycle count CY in each charge/discharge cycle becomes greater as a discharge depth DD increases. The healthy parallel number NPH is derived by multiplying a healthy parallel number NPHR of a reference block by the ratio of a capacity CPR of the reference block to a capacity CPS of a target block.

Abstract: An end-of-discharge voltage correction section subtracts, from an end-of-discharge open voltage, the product I×RO of a discharge current I of a block and an ohmic resistance RO of the block and the product ITD×RP of a discharge current ITD obtained by performing a time delay process on the discharge current and a polarization resistance RP of the block. Then, a resulting value is set as an end-of-discharge voltage VL. The ohmic resistance RO is increased as an equivalent cycle count CY increases, and is increased as a healthy parallel number NPH decreases. An increment ?CY of the equivalent cycle count CY in each charge/discharge cycle becomes greater as a discharge depth DD increases. The healthy parallel number NPH is derived by multiplying a healthy parallel number NPHR of a reference block by the ratio of a capacity CPR of the reference block to a capacity CPS of a target block.

Abstract: A current collector positive electrode enabling a NaS battery to be excellent in the charge recovery characteristic and low in internal resistance is provided, which collector has a high resistance layer formed by needle-punching glass fibers with 5 to 15 ?m fiber diameter into a felt substrate made of carbon fibers or graphite fibers by needle-punching from one surface of the substrate toward another surface of the substrate. The density of the glass fibers needle-punched into the substrate is gradually decreased in the direction from the above mentioned surface to the other surface of the substrate, and the deepest portions of the needle-punched glass fibers reach the depths of 85 to 100% of the substrate thickness.

Abstract: A current collector of positive electrode enabling a NaS battery to be excellent in the charge recovery characteristic and low in internal resistance is provided, which collector has a high resistance layer formed by needle-punching glass fibers with 5 to 15 &mgr;m fiber diameters into a felt substrate made of carbon fibers or graphite fibers by needle-punching from the one surface of the substrate. The density of the glass fibers needle-punched into the substrate is gradually decreased in the direction from the above mentioned surface to the other surface of the substrate, and the deepest portions of the needle-punched glass fibers reach the depths of 85 to 100% of the substrate thickness.