A lithium battery comprises at least one battery cell on a support, the battery cell comprising a plurality of electrodes about an electrolyte. A protective casing comprises a cover spaced apart from and covering the battery cell to form a gap therebetween with a polymer filling the gap. In one version, the polymer comprises polyvinylidene chloride polymer. First and second terminals extend out of the protective casing, the first and second terminals being connected to different electrodes of the battery cell.