ADU Battery-Ready Requirements Under the 2025 Energy Code
A newly constructed detached ADU must be battery-ready only when the electrical service to the unit is greater than 125 amps. At 125 amps or less the rule does not apply, and neither does it apply if a battery is actually installed with its wiring. Attached ADUs and conversions are additions or alterations, which do not take Section 150.0(s).
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Which service counts
Section 150.0(s) covers single-family buildings of one or two dwelling units whose service from the load-serving entity is greater than 125 amps. Exactly 125 amps is out; 150 amps is in. The compliance manual notes the 2025 change may exclude smaller ADUs. A battery is never required: the rule only prepares the electrical system for one.
What battery-ready means
Four items apply together. First, either BESS-ready interconnection equipment with 60 amps of backed-up capacity, or a dedicated raceway of at least 1 inch from the main service to a subpanel labelled "Subpanel shall include all backed-up load circuits"; the manual allows both. Second, four branch circuits at one panelboard: one for the refrigerator, one lighting circuit near the primary exit and one for a sleeping-room receptacle, the fourth being free. Third, a main panelboard busbar rated at least 225 amps. Fourth, space for a transfer switch within 3 feet of the main panel, with raceways run to it. Equipment detail is on JA12 battery storage.
The 200-amp panel trap
A 200-amp panel passes only if its busbar is rated 225 amps and that rating is marked. The Energy Commission says to look on the panel's interior metal surface or the door label; with no separate busbar rating the busbar equals the panel rating and the panel fails. An ADU subpanel fed from the main house panel does not need its own 225-amp rating if the main panel's busbar has it, as the panel upgrade page also notes.
Installing a battery instead
The exception to Section 150.0(s) applies when a battery system is installed with all the wiring and components for a fully operational system. The battery is then documented on form CF2R-PVB-02-E, and a battery chosen to earn compliance credit must also meet JA12.
Where else it matters
Attached ADUs and conversions follow the rules on the attached ADU page. For a detached unit see the detached ADU report and ADU solar. Reports start from the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
If the electric service for the ADU is 125 amps or less, the rule does not apply. Where a larger ADU subpanel is fed from the main house panel, the Energy Commission says the main panel's 225-amp busbar can satisfy it.
No. Battery-ready equipment only prepares for one, and installing a fully wired battery system satisfies the requirement in its place.
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View all ADU and JADU guides → · Permits and Compliance · Title 24 guide