Not everyone agrees that the battery fix Boeing has devised, and the FAA has approved, is a long-term solution. Some doubt that lithium-ion batteries are fit to fly at all.
Boeing has a two-fold response. Airlines are accustomed to replacing failed batteries, so the prospect that the li-ion batteries on a 787 might fail is not, in and of itself, an issue. In fact, chief 787 engineer Mike Sinnett is quite clear that he expects the batteries to fail.
But if they do fail in what is called a thermal runaway that produces extreme heat, the solution Boeing has designed to a)contain the heat inside a stainless steel box and b)prevent fire by using a venting system to rob the box of oxygen, will prevent such a failure from becoming a safety-of-flight issue.
In this article in Barrons, Will Boeing's Battery Fix Fly?, Jonathan Liang presents another view.