The mystery of potentially dangerous lithium ion batteries continues to hang over sales of vehicles using this technology. Experts who recently testifyied before the US National Transportation Safety Board (NTSB) said that failure of the technology has slowed development of electric cars and other applications of the batteries.

The crisis faced by Boeing in January over its 787 Dreamliner jet was also a major theme during the hearings. NTSB is investigating a battery fire that occurred on board one of the Dreamliners.

About 25 percent of a typical li-ion battery cell is flammable.

Analysts have not taken the reliability factor seriously enough in their sales forecasts – projections "were off by more than a factor of 10" when compared to the actual market size in 2011, said Yet-Ming Chiang, a professor of materials science and engineering at the Massachusetts Institute of Technology, to NTSB. The market has been very stressful for battery makers as many of them have gone out of business when the li-ion market failed to materialize.

Chiang said that about 25 percent of a typical li-ion battery cell is flammable. The batteries do need to become safer, but not at the cost of losing performance, said Glen Bowing, vice president of sales at Saft Specialty Battery Group. Thus, battery companies are exploring other technologies outside of li-ion in the hope of finding a safer, less costly solution. Boeing's crisis prompted rival jetmaker Airbus to drop li-ion batteries from its upcoming A350 jet. Tesla Motors and SpaceX chief Elon Musk said the lithium cobalt oxide cells used in the 787 Dreamliner are "fundamentaly unsafe" and packed too close together; if one cell catches fire, the entire battery pack could ignite in a chain-reaction scenario.

Fisker Automotive had its own notorious episodes with li-ion battery technology. Other automakers had their share of woes, too. Last year, Chrysler had the batteries in three of it Ram 1500 pickups overheat. Last month, Mitsubishi stopped production of its Outlander plug-in hybrid and a version of the all-electric i-MiEV. Two separate incidents – both in Japan – involved plug-in vehicle battery-pack fires that prompted investigation and suspension of the production lines.