Two major safety incidents involving Boeing 787 Dreamliners have caused two Japanese airlines to ground their fleets of the aircraft. The problems may be linked to a battery chemistry that’s particularly prone to causing fires.

Earlier today, a plane in Japan was forced to make an emergency landing after reports of a battery warning light and burning smell. Last week, a battery caught fire on a plane on the ground in Boston. In both cases, the problems may be related to Boeing’s decision to use a kind of lithium-ion battery chemistry that overheats and catches fire more readily than others.

It’s not yet clear whether the problems in the 787s originated with the batteries. Faults in the electronic controls have been implicated in other lithium-ion battery fires. According to reports, inspectors found liquid leaking from the 787’s batteries after the forced landing in Japan today. The battery was also discolored, but it wasn’t clear if it had caught fire.

Lithium-ion batteries have been known to cause fires in cell phones, laptops, and electric vehicles. But such problems are extremely rare, and usually result from damage to the battery—such as piercing or overcharging—or problems with the manufacturing process that introduce flaws in the cells.

Boeing’s 787 is the first commercial aircraft to use lithium-ion batteries, according to GS Yuasa, the Japanese battery manufacturer that supplies the batteries. The company also supplies batteries for the International Space Station and electric railcars, among other applications.

The chemistry—and safety—of lithium-ion batteries varies. According to GS Yuasa’s website, the batteries it uses for Boeing’s 787 use lithium cobalt oxide electrodes. These are known for high-energy storage capacity, but other battery chemistries, such as lithium iron phosphate, are more resistant to overheating. Because of safety concerns, many electric vehicle makers have shifted to alternative chemistries, sacrificing some energy storage capacity.

Because the electrolyte materials used are flammable, no lithium-ion batteries are completely safe. Some companies are developing a version that doesn’t use these electrolytes (see “Solid-State Batteries”). Consequently, battery makers install various safety features, including electronics designed to prevent overcharging. They also often include sensors and cooling systems.

According to GS Yuasa, its battery for the 787 “comes with battery management electronics which guarantees multiple levels of safety features.” A specification sheet for the batteries warns, “Inappropriate handling or application of the cells can result in reduced cell life and performance, electrolyte leakage, high cell temperatures, and even the possibility of smoke generation and fire.”

Boeing declined to comment on its selection of battery chemistries. A spokesperson says it is aware of the incident in Japan and is working with the airline and regulatory bodies to address it.