"We have a real opportunity here to really drive this to be the unified standard for North America, which I think will even enable more mass adoption," Barra said.

She told CNBC last week that GM expects to save as much as $400 million by working with Tesla's network. GM has said it would invest $750 million on charging infrastructure in the U.S. and Canada.

"This arrangement alone, this collaboration that we're doing, nearly doubles the amount of chargers that our GM customers will have access to," Barra said of Tesla. The savings come "because we've been able to do it faster and more effectively, and we're really looking for ways that we can be more capital-efficient as we go forward."

GM will build Tesla's North American Charging Standard connectors into its EVs starting in 2025, the automaker said. GM will weave Tesla's Supercharger network into its vehicle and mobile apps.

In late May, Ford said it would give its EV owners access to Tesla's Superchargers starting next spring through adapters. Ford also will stop building EVs with traditional Combined Charging System ports starting in 2025, instead using the port used by Tesla.

Barra noted during last week's Twitter Spaces conversation that "the three U.S.-based auto companies are all on one standard."

Automakers are trying to improve the charging experience before they launch EVs in high volumes. Nationwide, 1 in 5 charging attempts failed last year, according to J.D. Power. Tesla's Supercharger network tends to have much better charger uptime than peers. Fewer Tesla drivers face charger outages and, if a charger is down, the driver typically finds a working charger at the same location, the firm said in February.

Musk, who has complained about not receiving enough credit from the Biden administration for advancing EV adoption, vowed that his chargers will not discriminate between Tesla vehicles and those of other manufacturers.

"You have our full support, and we're incredibly excited to partner with you on this and just really make it a fantastic electric vehicle experience, whether somebody is driving a car from GM or from Tesla," Musk told Barra during the announcement on Twitter, which he owns.

Tesla's decision to open its network to Ford and GM electric vehicles "almost certainly will" affect the charging standard, said Mike Ramsey, an analyst covering automotive and transportation at Gartner.

"This is kind of like the equivalent of Samsung saying, 'OK, we're going to start using an Apple Lightning charger,' " Ramsey said. "It clearly is going to have a significant impact on the charging networks. They're going to effectively be forced into adopting this charging head, or they're going to lose business."

Ramsey said the debate over charging standards is not necessarily an example of the best technology winning, but more about market realities.

"Most electric cars getting charged out there are already using the Tesla standard — because they're mostly Teslas," Ramsey said. "It's easy to lose sight of the fact that Tesla has like 70 or 80 percent market share of EV sales. They are the de facto winner, even if GM and Ford didn't do this."