A bioelectric battery may be used to power implantable devices. The bioelectric battery may have an anode electrode and a cathode electrode separated by an insulating member comprising a tube having a first end and a second end, wherein said anode is inserted into said first end of said tube and said cathode surrounds said tube such that the tube provides a support for the cathode electrode. The bioelectric battery may also have a membrane surrounding the cathode to reduce tissue encapsulation. Alternatively, an anode electrode, a cathode electrode surrounding the cathode electrode, a permeable membrane surrounding the cathode electrode. An electrolyte is disposed within the permeable membrane and a mesh surrounds the permeable membrane. In an alternative embodiment, a pacemaker housing acts as a cathode electrode for a bioelectric battery and an anode electrode is attached to the housing with an insulative adhesive.