A packaged battery (10) and method of producing such is provided having a thin film lithium battery cell (11) sealably encased within a packaging layer (12). The battery cell (11) includes a substrate (13), an anode (16), an electrolyte (15), a cathode (14), a passivation layer (19), an anode current collector (17) and a cathode current collector (18). The packaged battery is produced by heat sealing a packaging foil (21, 22) to the exterior surfaces of the battery cell (11).