A battery pack is provided. In the battery pack, batteries and a circuit are completely separated. A battery block includes a battery package that can house one or more of the batteries. The circuit block includes a measurement/protection circuit that has a measurement function about use conditions or performance of the batteries or a function to protect the batteries that is housed in a circuit package wherein the battery block and the circuit block are fit in and housed inside of an outer case. The battery block and the circuit block can be independently removed and replaced from the outer case. In this regard, where a defect of the battery block or the circuit block occurs in a manufacturing process, the block with the defect can be replaced on its own. When the batteries in the battery block are deteriorated or consumed, the battery block can be replaced on its own. An electrolytic solution leaked from the batteries remains in the battery package.