An active metal that should be considered as an anode material in high energy density batteries is definitely magnesium. It is relatively cheap, much safer to use and handle than lithium, and its compounds are usually non-toxic. Similar to lithium, magnesium is covered by surface films in any 'inert' atmosphere that contains atmospheric contaminants, and in most of the relevant electrolyte solutions for batteries. In contrast to lithium where the surface films covering the active metal are Li-ion conductors, surface films formed similarly an magnesium cannot conduct the bivalent Mg2+ ions. We developed new electrolyte solutions based on ethers of the 'glyme' family and magnesium aluminates whose electrochemical window is 2.5 V wide. The efficiency of Mg deposition-dissolution cycles in these solutions is higher than 99%. We also showed that it is possible to construct rechargeable Mg batteries using these electrolyte solutions and cathodes of the MgxMoSy type (chevrel phase), which operate at 1-1.5 V, and can deliver more than 1000 charge-discharge cycles. Some technical details of these battery systems are discussed.