Australia’s Full Federal Court, in The NOCO Company v Brown and Watson International Pty Ltd [2026] FCAFC 44, has confirmed that applicants for divisional patent applications have an obligation to disclose the best method known to them at the filing date of the divisional application.
The decision has major implications for patent filing and litigation strategy in Australia, and is expected to expose some granted divisional patents to an increased risk of revocation.
The best method disclosure obligation in Australia
A notable feature of Australia’s patent legislation, different from most jurisdictions, is that a patent may be revoked if the complete specification does not “disclose the best method known to the applicant of performing the invention”: Patents Act 1990 ss 138(3) and 40(2)(aa).
This is a separate legal requirement from the sufficiency of disclosure obligation common to most patent laws, which is met if the invention is disclosed “in a manner which is clear enough and complete enough … to be performed by a person skilled in the relevant art”: Patents Act 1990 s 40(2)(a).
Over the past decade, Australian courts have stringently applied the best method disclosure obligation, revoking multiple patents based on evidence of information withheld about a preferred embodiment, even if that information pertained to an unclaimed feature or could have been derived by a person skilled in the relevant art without undue burden (i.e. the disclosure was “sufficient”).[1] Revocation under the best method ground of invalidity is now a powerful defensive tool available to infringers, particularly since deficiencies cannot be corrected by amendment.
Divisional applications
A patent applicant’s knowledge of the invention may change over time, for example as the patented technology progresses from concept to commercial product. Therefore, a critical question is: what date should be selected for ascertaining the best method to be disclosed? The courts have previously held that the relevant date is the filing date, being the international filing date for PCT-derived applications[2].
However, the situation for divisional applications has, until now, been unclear: is the applicant’s knowledge of best method to be assessed at the filing date of (i) the divisional application (as found in Dometic v Houghton Leisure Products[3]) or (ii) the earliest parent (e.g. PCT) complete application (as found at trial in NOCO v Brown and Watson[4])?
The NOCO v Brown and Watson litigation
NOCO sued Brown and Watson (“B&W”) for infringement of three Australian patents with filing dates in 2020-2022, all divisionals of a PCT application filed 3 July 2014. B&W cross-claimed for invalidity on grounds including lack of best method disclosure.
The patents in issue related to a vehicle jumpstarter which included a battery for supplying power and a power switch for connecting the jumpstarter to a vehicle battery. The evidence indicated that NOCO re-designed the commercial embodiment of its invention in December 2014 (after the PCT filing date), increasing the size of the lithium ion battery and replacing the power FET switch with a relay switch to address various practical problems. The trial judge concluded that the re-designed apparatus represented a best method known to NOCO before the divisional filing dates, but there was nevertheless no failure to disclose best method because the relevant date for ascertaining the applicant’s knowledge was the PCT filing date.
Decision on appeal
The appeal judges reviewed the statutory scheme and case law relevant to the date for ascertaining best method knowledge.[5] In a revocation action, the specification that must comply with the disclosure requirements – both best method and sufficiency – is the specification of the patent in suit, not an earlier-filed PCT specification from which priority is claimed. Moreover, the applicant of a divisional application and the corresponding PCT application may be different, e.g. due to assignment. Both factors weighed in favour of the relevant knowledge date being the date of filing the divisional specification.
NOCO relied on Rescare in support of its position. In that case, Gummow J expressed the view that “the adequacy of the disclosure should be judged by reference to the time from which dated the monopoly granted the applicant in exchange for the disclosure”.[6] Because the monopoly conferred by a divisional patent commences at the PCT filing date, NOCO submitted that same date applies to best method knowledge.
The appeal court rejected this submission, noting that the dispute in Rescare was whether the relevant date for best method disclosure in a PCT application was its filing date or a later publication date. Gummow J had already concluded that the PCT filing date applied. His obiter remarks merely demonstrated that there was no inconsistency between this outcome and the commencement of the monopoly, and did not support a general proposition that the best method known at the commencement of the patent term must be disclosed.
The appeal court thus held that NOCO’s divisional patents were invalid for failure to disclose the best method known to the applicant at the divisional filing dates, overturning the trial judge’s decision on this point. Other grounds of invalidity made out at trial were confirmed by the appeal court.
Takeaway points
The outcome is of great significance to patent applicants in Australia. It is now clear that applicants must add disclosure about the current best method to a divisional patent specification if the invention has materially evolved since filing the parent (PCT) application. Ostensibly, it may be necessary to disclose detailed information about optimisations in commercial embodiments (planned or realised), or even about further patentable inventions falling within the claim scope. There is a real risk that withholding such information from a divisional application, whether as a trade secret or unintentionally, could lead to invalidation of the patent.
Patent applicants should thus be very cautious about abandoning or limiting inventions disclosed in a parent application in the hope of pursing this subject matter in a divisional, considering the possibility that a burdensome new disclosure obligation may arise.
More positively for patent applicants, the appeal decision confirms that best method failures in a complete (PCT) application can be remedied in a divisional application – provided the applicant is willing to disclose its latest knowledge of best method.
Advice available
POF patent attorneys and litigators are well-equipped to advise our clients about best method and other complexities of patent filing and litigation strategy in Australia. Please contact us with any questions.
[1] Les Laboratoires Servier v Apotex Pty Ltd [2016] FCAFC 27; Sandvik Intellectual Property AB v Quarry Mining & Construction Equipment Pty Ltd [2017] FCAFC 138
[2] Rescare Ltd v Anaesthetic Supplies Pty Ltd [1992] FCA 811; Pfizer Overseas Pharmaceuticals v Eli Lilly & Co [2005] FCAFC 224
[3] Dometic Australia Pty Ltd v Houghton Leisure Products Pty Ltd [2018] FCA 1573
[4] The NOCO Company v Brown and Watson International Pty Ltd [2025] FCA 887
[5] The NOCO Company v Brown and Watson International Pty Ltd [2026] FCAFC 44 at 205-223.
[6] Rescare Ltd v Anaesthetic Supplies Pty Ltd [1992] FCA 811 at 133-135.
