Retired Boeing engineer Chris Johnson spent much of his career focused on developing battery technology for the company's planes.
The lithium-ion battery used in the 787 is similar to the batteries powering millions of smartphones and laptops, only much larger. They are needed to start the plane's engines in the absence ground power or in a situation where an engine restart is needed in mid-air.
Lithium-ion batteries pack more punch than older battery technologyies, and they are lighter and more environmentally friendly. But as with any battery type, they carry a risk.
Lithium-ion batteries can overheat to the point of starting a fire, which is what happened to a Japan Airlines plane in Boston last week and is suspected of being the cause of the incident early Wednesday on an All Nippon Airways 787 flying between two Japanese cities.