The Best Method Requirement: Australia's Quiet Patent Killer — and What NOCO Just Changed

Most patent validity attacks are about what the world already knew: was the invention new, was it inventive? The best method requirement is different. It's about what you knew and didn't say. And following the Full Federal Court's decision in The NOCO Company v Brown and Watson International Pty Ltd [2026] FCAFC 44, it may become one of the most dangerous validity traps in Australian patent law, particularly for divisional applications.

What is the best method requirement?

Under s 40(2)(aa) of the Patents Act 1990, a complete specification "must disclose the best method known to the applicant of performing the invention." The rationale is the patent bargain itself: in exchange for a monopoly, the public must receive a full and honest disclosure. As courts have long put it, an applicant must not get the benefit of a patent while deliberately, or even inadvertently, keeping the best way of working the invention to itself.

Three features of the doctrine, reflected in IP Australia's Patent Manual of Practice and Procedure (§5.6.7.5), matter most for patent owners:

1. It's subjective. The related sufficiency requirement asks objectively whether a skilled person could perform the invention. Best method asks what this applicant actually knew when it filed. There is no defence that the better method was common general knowledge or self-evident. In the Manual's words, "the applicant must disclose the best method known to them."
2. It's about what's material. You don't need a section headed "best method," and describing one method is generally enough. But the specification must include those aspects of the method that are material to the advantages the invention is claimed to bring. If your invention promises safety and reliability, and you know a particular component delivers those advantages better than the one described. That knowledge belongs in the specification.
3. It's invisible until it's fatal. Here is the feature clients find most surprising. IP Australia's examiners will not catch a best method defect. As the Manual candidly explains, evidence of what an applicant privately knew "is generally not available during examination," so any method the applicant describes is treated as the best method, and real challenges "are likely to arise during opposition proceedings rather than during examination." Nor can the defect usually be fixed later: adding the withheld method to the specification would generally add new matter, which s 102(1) prohibits. The result: a best method failure sails silently through examination and grant and detonates years later in opposition or revocation proceedings, where it can invalidate every claim.

The NOCO case: when "later" becomes "too late"

NOCO, a US company, held three Australian patents for lithium-battery jump starters with a safety feature preventing sparking and reverse-polarity damage. All three were divisional applications filed in 2020, 2021 and 2022, stemming from a PCT application filed back in July 2014. When NOCO sued Australian distributor Brown and Watson for infringement, Brown and Watson counterattacked on validity, and best method became the silent issue of the case.

Within months of the 2014 PCT filing, NOCO learned that its commercial jump starter worked better with two changes: a larger battery, and replacing the FET switches described in the specification with relays, after the FETs proved unreliable. The battery and the power switch were the two core components of the device. Yet when NOCO filed its divisionals five to eight years later, the specifications still taught FETs and said nothing about the improvements. Indeed, NOCO broadened its divisional claims to cover any power switch, while withholding which switch it knew actually worked best.

The legal battleground was timing. Best method is assessed against the applicant's knowledge "at the time of filing the complete specification" — but for a divisional, which specification? NOCO argued the relevant date was the 2014 parent filing (when it knew nothing of the improvements). The trial judge agreed. The Full Court did not.

The Full Court's logic was rooted in the Act itself: a divisional application is its own complete application, with its own complete specification, so the best method obligation attaches to each divisional's specification, assessed at that divisional's own filing date. And to NOCO's complaint that this was unfair, the Court gave a pointed policy answer: a divisional applicant can enlarge its monopoly beyond the parent's claims as NOCO had done by deleting the FET limitation. It is not "unjustifiably asymmetrical" to require the disclosure to keep pace with the enlarged monopoly.

The consequence is that all asserted claims of all three patents were invalid for failure to disclose the best method including claims that had survived the other validity attacks. IP Australia has since updated the Patent Manual to state the rule expressly: for divisionals, "the relevant date is the filing date of the divisional application."

One point remains open. The Court wasn't asked to decide which date applies where a divisional descends through intermediate parent applications. For long divisional chains, that question awaits another case but no prudent filer should bet on a generous answer.

What this means for your business

Divisional filing is no longer a copy-paste exercise. Every divisional filing is, in effect, a fresh declaration that the specification discloses the best method you know today. Before filing, ask:

• Has our commercial product diverged from the patent's description? Are there different components, materials, formulations or configurations?
• Are any of those changes material to the advantages the invention claims to deliver?
• Are we broadening the claims? If so, the disclosure obligation is at its most acute.

Audit existing divisional portfolios before enforcing them. Divisionals filed years after their parents may carry latent best method risk. NOCO discovered its problem in litigation. As a consequence, NOCO left the courtroom with three invalid patents and an order to pay 85% of its opponent's trial costs, plus the costs of the appeal.

Don't rely on examination as a safety net. Your patents were granted; that says nothing about best method compliance. The defect only surfaces when someone with commercial motivation goes looking.

The bottom line

The best method requirement asks a simple, honest question: did you tell the Patent Office the best way you knew to perform your invention — on the day you filed? After NOCO, that question is asked afresh of every divisional. If your answer is "we filed the parent's text unchanged," it's time to talk to your patent attorney.