A nonaqueous-electrolyte battery which is capable of preventing introduction of water and deterioration in the capacity thereof is disclosed. The nonaqueous-electrolyte battery according to the present invention incorporates a case constituted by laminated films; and a unit cell which is accommodated in the case and having a structure that the peripheries of the case is sealed with heat, wherein when an assumption is made that the quantity of water capable of penetrating a heat-weld resin layer which is the innermost layer of the case having a thickness of T (.mu.m) is R (g/m.sup.2day), the cross sectional area of resin in a heat-sealed portion is S (cm.sup.2), an average width of the heat-sealed portion is W (cm) and the capacity of the unit cell is C (Wh), the following relationship is satisfied: (T.times.R.times.S)/(W.times.C).ltoreq.0.96 .mu.g/Whday. When the foregoing structure is employed, water introducing rate can be reduced to 350 .mu.g/year or lower per capacity (Wh).