is then applied over the complete photovoltaic cells 16 for covering and leveling the photovoltaic cells 16 except for contact areas 32 a 32 b the glue 30 is preferably applied by means of printing also a water absorbing getter material such as calcium oxide cao may be incorporated in the glue 30 to protect the cells 16 from moisture from the side of the device also a rim of standard glue not shown could be applied around the device except for the forthcoming battery to reduce water penetration and thereby further protect the device finally a prefabricated thin battery 34 is placed on top of the glue 30 one pole 38 a of the prefabricated battery 34 is connected to the contact area 32 a via a first connection 36 a and the other pole 38 b of the prefabricated battery 34 is connected to the contact area 32 b via a second connection 36 b thus the photovoltaic cells 16 a 16 b are connected in series to the battery 34 allowing the photovoltaic cells 16 to charge the battery 34 the battery 34 is prefabricated in a sense that incorporating the battery in the device mainly includes assembling the battery with the rest of the device no other coating or sealing has to be provided on top of the prefabricated battery 34 thus here the prefabricated thin battery 34 acts as a top side encapsulation of.