The present application provides a drug-delivery device comprising a drug reservoir chamber 16, containing a substance to be delivered, in fluid connection with a drug administration means 18, and an electrically-controlled battery unit 10 comprising at least one displacement-generating battery cell 19 coupled to the drug reservoir chamber 16 by a coupling means 14, the arrangement being such that the displacement derived from the battery unit 10 is conveyed by the coupling means 14 to the drug reservoir chamber 16 such that the substance is expelled from the drug reservoir chamber 16 towards the drug administration means 18.