The board of township trustees may agree with a corporation organized for charitable purposes and not for profit or with a municipal corporation for the erection and management of a hospital suitably located, for the treatment of persons of the township who are sick or have disabilities, or for an addition to such hospital, and for a permanent interest therein to such extent and upon such terms as are agreed upon between the board and such corporation. The board shall provide for the payment of the amount agreed upon for such interest, either in one payment or in annual installments, as agreed. Such agreement shall not become operative until approved by a vote of the electors of such township under section 513.06 of the Revised Code.