Although 85% is an exaggeration, Ars Technica noticed a 33% drop in battery life while using flash on a MacBook Air.

We did find (quite by accident) that Apple may have more reasons behind not installing Flash by default other than the stated reason of ensuring that users always have the most up-to-date version. Having Flash installed can cut battery runtime considerably—as much as 33 percent in our testing. With a handful of websites loaded in Safari, Flash-based ads kept the CPU running far more than seemed necessary, and the best time I recorded with Flash installed was just 4 hours. After deleting Flash, however, the MacBook Air ran for 6:02—with the exact same set of websites reloaded in Safari, and with static ads replacing the CPU-sucking Flash versions.
The future of notebooks: Ars reviews the 11" MacBook Air

That was done with just using ads on web pages and no video being shown.

Yeah, I don't think I or anyone else wants their battery life to drop by 1/3 just from stupid ads. Flash needs to die. And I'm glad Jobs did what he did in not allowing it on iOS which in turn is causing Flash to slowly go away.