This article outlines the basic chemistry of manganese and the structural feature and electrochemistry of manganese dioxide (MnO 2) in aqueous electrolytes. Because of its common usage in aqueous and nonaqueous battery systems such as zinc–carbon cells, alkaline MnO 2–Zn cells (primary and rechargeable (RAM)), and primary lithium cells, an overview of these battery systems is given. Rechargeable lithium-ion batteries with manganese-based positive electrodes (spinel and layered types) are also included. The use of the low-cost zinc–carbon battery (Leclanché and zinc chloride type) is still very important for developing countries. However, for advanced devices, alkaline MnO 2–Zn batteries are preferred, which use electrolytic manganese dioxide (EMD) and an alkaline electrolyte (KOH). Rechargeable alkaline Manganese cells are constructed similar to the primary alkaline type, but they are zinc-limited (‘one-electron’ discharge of MnO 2). Heat-treated EMD is applied in primary Li–MnO 2 batteries. Manganese-based materials such as LiMnO 4 (spinel) have been successfully used in lithium-ion batteries, as their poor performance at elevated temperature and capacity fading have been overcome. Stabilized layered lithium–manganese oxides and lithium–nickel–manganese oxides are very good alternatives to the currently preferred LiCoO 2 positive electrode. Different lithium-ion cell combinations are being investigated as ‘lead-free’ accumulators for future applications.