Tesla CEO Elon Musk on Sunday announced that the electric-car maker’s long-anticipated “Battery Day” event has been tentatively scheduled for Sept. 15, 2020. Musk has been promising the event for more than a year. It is expected to reveal significant advances in battery and battery production technology from Tesla and its partners.

The event has been delayed several times. Musk has previously said on Twitter that it is important for the event to be held in person, rather than virtually, a dicey proposition during the coronavirus pandemic. In his announcement Sunday, Musk said the event would include a tour of Tesla’s new battery cell “production system” in Fremont, Calif. Musk also clarified that despite previous plans, the event will not cover Tesla’s anticipated Plaid powertrain update.

Tesla seems likely to showcase at least two advantages of its evolving battery technology: cost and durability.

The automaker has long partnered with Panasonic to produce its batteries, but it has been working to establish in-house battery production, with a focus on scaling to reduce costs. A battery’s cost per kilowatt-hour of storage capacity is a key competitive factor in the electric vehicle market. More storage translates to higher range, a major consideration for prospective buyers of electric vehicles. But batteries are also the key determinant in the total cost of an electric passenger vehicle and whether it is price-competitive with a gas-burning car.

Tesla may also reveal more about its partnership with China’s Contemporary Amperex Technology (CATL), which supplies what are known as lithium iron phosphate (LFP) batteries. As reported by Reuters, the batteries eliminate expensive cobalt from their chemistry. The batteries can also reportedly last for more than 1 million miles of use and recharging, about three times as long as the current Model 3’s lithium-ion batteries. That would substantially reduce long-term operating costs.

Like most Tesla plans, Battery Day has been delayed multiple times—though for reasons well outside of Tesla’s control. At an April 2019 event showcasing the company’s self-driving tech, Musk said a similar event focused on battery and powertrain would take place in “about six months,” suggesting February or March of 2020. That was later pushed to April, then July—and now September—at least in part because of the coronavirus pandemic and the risks of gathering many people at a public event.

But Musk was clear that the Sept. 15 date is still tentative. The event could be derailed by the coronavirus yet again: Cases across the United States have been trending upward for two weeks now, and there is some concern that fall 2020 could see a renewal of widespread shelter-in-place orders.

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