Cal. Public Utilities Code § 776

(a) The commission shall, upon making the determination pursuant to subdivision (c), develop and implement performance reliability standards for all backup power systems installed on the property of residential and small commercial customers by a facilities-based provider of telephony services. Those standards shall do all the following: (1) Establish minimum operating life. (2) Establish minimum periods of time during which a telephone system with a charged backup power system will provide the customer with sufficient electricity for emergency usage. (3) Establish means to warn a customer when the backup power system’s charge is low or when the system can no longer hold a charge. (b) The commission, in developing and implementing any standards in accordance with subdivision (a), shall consider current best practices and technical feasibility for establishing battery backup requirements. (c) The commission shall not implement standards in accordance with this section unless it determines that the benefits of the standards exceed the costs.