Body-mountable device with a common substrate for electronics and battery

An example device includes a silicon substrate having a first substrate surface and a second substrate surface; a plurality of layers associated with one or more electronic components of an integrated circuit (IC), where the plurality of layers are deposited on the second substrate surface; a lithium-based battery having a plurality of battery layers deposited on the first substrate surface of the silicon substrate, where the lithium-based battery includes an anode current collector and a cathode current collector; a first through-silicon via (TSV) passing through the silicon substrate and providing an electrical connection between the anode current collector and the plurality of layers associated with the one or more electronic components of the IC; and a second TSV passing through the silicon substrate and providing an electrical connection between the cathode current collector and the plurality of layers associated with the one or more electronic components of the IC.