Widening a patent claim is never free. Every limitation you drop to capture more of the market quietly commits you to two things: a disclosure that actually supports the wider claim, and a priority date that can still carry it. Lose sight of either, and the broader claim becomes the weakest point in the portfolio. A recent Full Federal Court decision made the cost concrete — three jump-starter patents were held obvious, several claims lost their earliest priority date and fell for lack of novelty, and the patents failed Australia’s best-method requirement.

The strategic thread running through all three failures was the same: the patentee had broadened its divisional claims by removing specific limitations (a named switch type and a two-sensor arrangement), but the wider claims weren’t disclosed in the original PCT filing, so they slipped to a later priority date — and the Court confirmed that best method is assessed at the filing date of the divisional, not the parent, meaning improvements learned in the years between had to be disclosed and weren’t.

A claim is only as strong as the disclosure and the priority date underneath it, and “broader” and “stronger” are not the same thing. Three checks are worth running across any portfolio built on divisionals: first, does each broadened claim still trace to disclosure in the earliest application, or has it drifted to a priority date that exposes it to intervening prior art; second, where you widened a claim by stripping a limitation, did you disclose the best method known at the divisional filing date for that broader invention; third, are you filing divisionals to protect genuinely distinct inventions, or simply to keep options open in a way that manufactures risk.

Patentees should review portfolios for vulnerability to this ground and consider filing further divisionals to cure any later-discovered best method; international applicants are most exposed, since few jurisdictions outside Australia carry a standalone best-method requirement. Disciplined claim strategy, in the end, is knowing what not to claim — and knowing what you must disclose the moment you decide to claim it.

Read the case here: The NOCO Company v Brown and Watson International Pty Ltd [2026] FCAFC 44