(A)   Every person accused of an offense is presumed innocent until proven guilty beyond a reasonable doubt, and the burden of proof for all elements of the offense is upon the prosecution. The burden of going forward with the evidence of an affirmative defense, and the burden of proof by a preponderance of the evidence, for an affirmative defense, is upon the accused.
   (B)   As part of its charge to the jury in a criminal case, the court shall read the definitions of “reasonable doubt” and “proof beyond a reasonable doubt” contained in division (d) of this section.
   (C)   As used in this section, an “affirmative defense” is either of the following:
      (1)   A defense expressly designated as affirmative;
      (2)   A defense involving an excuse or justification peculiarly within the knowledge of the accused, on which he or she can fairly be required to adduce supporting evidence.
   (D)   “Reasonable doubt” is present when the jurors, after they have carefully considered and compared all the evidence, cannot say they are firmly convinced of the truth of the charge. It is a doubt based on reasonable and common sense. “Reasonable doubt” is not mere possible doubt, because everything relating to human affairs or depending on moral evidence is open to some possible or imaginary doubt. “Proof  beyond a reasonable doubt” is proof of such character that an ordinary person would be willing to rely and act upon it in the most important of his or her own affairs.
(ORC 2901.05)