Cal. EVID § 1107

(a) In a criminal action, expert testimony is admissible by either the prosecution or the defense regarding intimate partner battering and its effects, including the nature and effect of physical, emotional, or mental abuse on the beliefs, perceptions, or behavior of victims of domestic violence, except when offered against a criminal defendant to prove the occurrence of the act or acts of abuse which form the basis of the criminal charge.

(b) The foundation shall be sufficient for admission of this expert testimony if the proponent of the evidence establishes its relevancy and the proper qualifications of the expert witness. Expert opinion testimony on intimate partner battering and its effects shall not be considered a new scientific technique whose reliability is unproven.

(c) For purposes of this section, “abuse” is defined in Section 6203 of the Family Code, and “domestic violence” is defined in Section 6211 of the Family Code and may include acts defined in Section 242, subdivision (e) of Section 243, Section 261, 273.5, 273.6, 422, or 653m of, or former Section 262 of, the Penal Code.

(d) This section is intended as a rule of evidence only and no substantive change affecting the Penal Code is intended.

(e) This section shall be known, and may be cited, as the Expert Witness Testimony on Intimate Partner Battering and Its Effects Section of the Evidence Code.

(f) The changes in this section that become effective on January 1, 2005, are not intended to impact any existing decisional law regarding this section, and that decisional law should apply equally to this section as it refers to “intimate partner battering and its effects” in place of “battered women’s syndrome.”