This story includes reporting from the Associated Press

U.S. safety regulators have opened an investigation into electric and hybrid vehicle batteries after five automakers issued recalls due to possible defects that could cause fires or stalling.

The National Highway Traffic Safety Administration said the probe covers more than 138,000 vehicles with batteries made by LG Energy Solution of South Korea.

General Motors, Mercedes-Benz, Hyundai, Stellantis and Volkswagen have issued recalls since February of 2020, mostly due to internal battery failures that can increase the risk of fires.

The agency said it will write to LG and other companies that might have bought similar batteries to make sure recalls are being done when needed.

Messages were left on April 5 by the Associated Press seeking comment from LG Energy Solution.

The investigation is another bug in a growing global rollout of electric vehicles by all automakers to replace internal combustion vehicles to cut emissions and fight climate change. Ford and BMW also have recalled batteries in recent years. Also, the U.S. National Transportation Safety Board investigated a series of fires in Tesla vehicles and said the high-voltage lithium-ion batteries pose safety risks to first responders after crashes.

Many governments are counting on counting EVs to replace gasoline-burning vehicles that emit greenhouse gases that cause global warming.

Data on electric vehicle fires is limited, but a small sample in April of 2021 by the insurance industry’s Highway Loss Data Institute found that EVs and their conventional gas counterparts had about the same number of non-crash fire claims per 1,000 insured vehicle years.

The institute tracked claims for 10 EVs and their gas equivalents and found that EVs had 0.19 fire claims per 1,000 insured vehicle years compared with 0.2 for gasoline counterparts.

In a document posted on its website, NHTSA said the recalls began on Feb. 24, 2020 when Mercedes recalled a 2019 Smart Fortwo electric vehicle. The company said the high-voltage battery made by LG had a defect that could ignite inside the battery cells, raising the risk of a fire.

Eight months later, Hyundai recalled some 2019 and 2020 Kona EVs with a similar problem.

In November of 2020, General Motors began a string of recalls that involved more than 140,000 Chevrolet Bolt EVs from the 2017 through 2022 model years due to the “simultaneous presence of two rare manufacturing defects in the same battery cell.” The defect caused at least 10 fires, causing GM to warn owners to park the Bolts outdoors. LG Energy Solution agreed to reimburse GM $2 billion for the recall costs, and the company remains in a joint venture with LG to build batteries for its next generation of electric vehicles. This month, GM is scheduled to restart production and sales of Bolts with replacement battery cells.

Hyundai issued a second battery recall March of 2021 covering 2019 and 2020 Konas and 2020 Ioniq EVs and said an electrical short inside the batteries could increase the risk of fires while parked, charging or driving.

Last February, Stellantis’ Chrysler brand recalled some 2017 and 2018 Pacifica plug-in hybrid minivans with LG batteries after getting a dozen reports of fires. A month later, VW recalled some 2021 ID4 electric vehicles with unreliable connections inside the batteries that could cause stalling. Stellantis also has a joint venture with LG Energy Solution to make batteries for future electric vehicles.

In 2020, Utility Arizona Public Service (APS) announced the completion of a far-ranging investigation into what has been considered as one of the most significant battery storage fires in US history which injured four firemen in Surprise, Arizona, on the night of Friday, 17 April 2019.

The NHSTA probe of LG electric vehicle batteries spurs flashbacks to what’s considered one of the most significant battery storage fires in U.S. history— an incident also linked to LG.

In July 2020, Arizona Public Service (APS) released details of a wide-ranging investigation into a fire that injured four firemen at the McMicken Energy Storage Facility in Surprise, Arizona in April 2019.

The fire was caused when a rack of lithium-ion batteries supplied by LG Chem, and operated by storage company Fluence, heated up and caught fire, according to the report. The fire suppressant deployed to douse the fire proved ineffective, leading to a build-up of explosive gases that ignited when firefighters opened a door, sending several to the hospital.

The report noted with a reasonable degree of scientific certainty that the failure was caused by an internal cell defect, specifically abnormal lithium metal deposition and dendritic growth within the cell.

Investigators categorized the incident as a “thermal runaway event.” The incident cascaded and propagated from cell 7-2 through every cell and module in Rack 15, via heat transfer. This propagation was facilitated by the absence of adequate thermal barrier protection between battery cells, which may have stopped or slowed the propagation of thermal runaway, according to the report.

Approximately three hours after thermal runaway began, the BESS door was opened by firefighters, agitating the remaining flammable gases, and allowing the gases to make contact with a heat source or spark.

LG Chem later refuted the findings of the APS investigation, which was prepared by DNV-GL, with their own analysis from Exponent.

In comments filed with the Arizona Corporation Commission, LG Chem called into question DNV-GL’s investigatory process and conclusions. The company’s 162-page rebuttal said that a “reasonable degree of scientific rigor, together with relevant peer reviewed literature, rule out the initiating cause proposed by DNV-GL” as LG’s independent analysis could not produce evidence of metallic lithium plating as the cause of the thermal runaway.

LG’s analysis blamed an external heat source for initiating the thermal runaway, not an internal cell failure.

LG Energy Solution provided batteries for Vista Corp.’s Moss Landing Energy Storage Facility in California. A malfunctioning heat suppression system caused an incident forced the Phase I (300 MW/1,200 MWh) facility offline in September.

The facility uses a heat suppression system that protects against thermal runaway in individual battery modules. That system’s preaction zones consist of carbon steel header pipes that are connected by flexible hoses to rack piping, which has sprinkler nozzles that are inserted into each battery module.

The design calls for the release of water in a particular zone upon detection of certain levels of smoke by the Very Early Smoke Detection Apparatus (VESDA). After release, water is then be injected into a battery module if the temperature in that module becomes too high.

The investigation found that in response to detection of very low levels of smoke in one area of the facility, the heat suppression system activated.

The findings report said some of the water was sprayed directly onto the battery racks, and some of it leaked through gaps in the upper floor onto racks located on the lower floor. In total, roughly 7% of the battery modules and other facility systems were damaged.

Shortly after the September incident, Vistra officials said they didn’t believe the system’s lithium-ion batteries were the cause. The company said when water was first released to the heat suppression system, all battery module temperatures were recorded as “within established temperature limits and well below the level that would indicate a thermal runaway.”