Early models of the all-electric 2021 Mustang Mach-E have a battery issue that may leave owners struggling to start their vehicles despite its being fully charged, according to a technical service bulletin that Ford sent to federal regulators.

"Bad software is turning some Mustang Mach-Es into 'electric bricks,'" said a headline in TheVerge.com, a tech website that first reported news of the Mach-E battery problem last week. The brick term has been coined by Mach-E forum members seeking advice from one another online.

The March 25 technical service bulletin filed with the National Highway Traffic Safety Administration describes the situation in more technical terms: "12-Volt Battery Becomes Discharged While The Vehicle Is Plugged In During The High Voltage Charging Process."

Discharging, or draining, describes the process of a battery losing energy.

When this happens, Mach-E customers get notified by their FordPass app that the Mach-E is in "deep sleep" mode, TheVerge noted.

The issue affects vehicles built on or before Feb. 3, Ford said. While the company has touted the potential for over-the-air updates, this fix requires a dealer visit.

The Ford bulletin said the problem may be related to the powertrain control module. The company told Reuters the situation is a "software glitch, which results in the small battery discharging while a larger high-voltage battery pack is charging."

The Dearborn, Mich., automaker declined to say how many Mach-E owners are affected. The company reported selling three vehicles in December, 238 in January and 3,739 in February.

"We are aware that a small number of Mustang Mach-E owners have had their 12-volt battery reach a low-voltage condition. We proactively worked with early owners experiencing this issue to identify the root cause and a fix," said Ford spokeswoman Emma Bergg. "In the rare instances where this still occurs, customers can now contact their local EV-certified Ford dealer to have the matter resolved."

On Jan. 17, the Detroit Free Press reported that Ford was holding the Mach-E for additional quality review. Bergg estimated the hold would last up to eight weeks for "several hundred" vehicles after being built at the factory in Cuautitlan, Izcalli, Mexico.

On March 2, Ford notified thousands of Mach-E customers they would be compensated for their patience as the company continued its quality checks.

By mid-March, some customers in Norway reached out about delivery delays.

"We began deliveries in the U.S. at the end of 2020, as planned, and are on track to begin deliveries starting in spring in Europe," Bergg said at the time. "Ford is committed to delivering a high-quality vehicle, so delivery timing will vary by market."

The Mach-E is especially valuable vehicle to Ford as its debut vehicle designed to challenge Tesla, the dominant player in the all-electric market.

The Mach-E won 2021 North American Utility of the Year and a Morgan Stanley analyst said first quarter sales illustrate a horserace with Tesla. Ford said it sold 6,614 Mach-E SUVs. Meanwhile, Tesla reported 184,800 vehicles sold during the first three months of the year, twice as many as a year ago, with strong demand in China.

F-150 battery woes

This Mach-E situation is the second battery-related issue raised with Ford on new products in 2021. Some customers and dealerships saw dead 12-volt batteries on the brand-new 2021 Ford F-150 pickups due to phantom battery drain, as first reported on Feb. 15 by the Free Press.

"A population of vehicles built before we began shipping to dealers require a software update to prevent batteries from losing their charge," Ford spokesman Said Deep said at the time.

He said Friday that the battery issues had no relation to one another, as he understands the situation.

Ford declined to explain why the 12-volt batteries were losing juice or how many vehicles potentially were had a problem.

"My truck went into deep sleep mode once and the only way to bring it back to life was a jump start," one F-150 owner wrote on a forum. "Had to use the physical key in the fob to open the door."

That situation also required a visit to the dealership for a software update.

The F-150 was held for additional quality updates, too.

Mach-E repair instructions

Fixing the Mach-E battery cannot be done at home as it requires specific software programs. Ford explicitly writes in the service bulletin: "The procedures should not be performed by 'do-it-yourselfers.' "

This is the protocol for professional technicians:

—Connect a battery charger to the 12-volt battery.

—Verify that the negative cable of the charger is installed on a chassis or engine ground, and not the 12-volt battery negative terminal to prevent the battery saver mode from activating on the vehicle. Do not have the vehicle plugged into the High Voltage battery charger during programming. This can cause modules to not program correctly. Only have the 12-volt battery charger installed.

—Reprogram the powertrain control module using the latest software level of the appropriate Ford diagnostic scan tool.

—Updating only one module at a time, check the secondary onboard diagnostic control module; the battery energy control module; the secondary onboard diagnostic control module B; the secondary onboard diagnostic control module C; and the antilock brake system.

Software problems have presented ongoing headaches for automakers globally and often come up in consumer satisfaction surveys and reports to federal safety regulators.