Battery

A battery with a high battery voltage at charging and improved energy density is provided. A cathode (12) and an anode (14) are laminated with a separator (15) sandwiched therebetween which is impregnated with an electrolyte. The cathode (12) has a cathode active material including a lithium composite oxide which contains lithium, at least either cobalt or nickel, and oxygen. The battery voltage at charging is 4.25 V or more. The moisture content in the electrolyte is 20 ppm mass ratio or less to the electrolyte. This inhibits metal eluting from the lithium composite oxide even at high voltages.