Writing about solid-state batteries feels like waiting for a train that's always five minutes away, but it never actually arrives. Automakers have been developing these 'holy grail' batteries for years, but we're yet to see a real-world mass-market application.

The bold claims, however, continue to land much faster than the tech itself. But what their makers intend to do with this technology can speak volumes as well. At the recently concluded Japan Mobility Show, Toyota said that its solid-state batteries are designed to last 40 years.

If that's true, that would be about 2.7 times the average age of a passenger vehicle in the U.S. as of 2025, which now stands at 14.5 years according to the Bureau of Transportation Statistics.

Keiji Kaita, the president of Toyota's Carbon Neutral Advanced Engineering Development Centre, explained these goals to the Australian news outlet Car Expert.

"The existing lithium battery we are making now, by the typical usage, our target is maybe 10 years, 90% capacity," Kaita said. "This [SSB] is maybe 40 years, 90% capacity—this is the potential we are targeting." If what Toyota says is true, it could radically change how batteries are made and used in vehicles.

Kaita told the outlet that while the cost of these batteries could be greater upfront, over time, they would make up that difference with longevity. "So initially, indeed, the price is much higher—but gradually that will get close to others—but we'd like to use the long-life, super long-life [lifespan] features," he said.

Automakers and battery experts have long said that solid-state batteries can deliver longer range, reduce the pack weight significantly and improve the cells' safety profile, meaning the fire risk could be lower. Theoretically, these batteries will also be faster-charging and more durable.

Battery makers also say these new packs will last far longer, with Toyota claiming its 40-year all-solid-state battery will retain 90% of its original capacity by the end of that timeframe. Currently, automakers typically offer eight-year warranties on their high-voltage packs. Tesla has previously said that on average, its lithium-ion batteries can last 200,000 miles with about 90% capacity retention.