Except it’s not here, even though ‘solid-state will save the day’ stories have been regularly popping up for the past few years. Toyota first showed a solid-state prototype in 2010 and said it would commercialise the tech by 2020. Five years later we’re still waiting, and despite BMW and Mercedes talking-up on-road tests this year, both are still years away from fitting solid-state tech to a production car.

So what’s going on? When are we going to get our hands on these mythical batteries? What’s the science behind the sorcery? And why is it taking so long to get here?

Modern electric cars make pioneer EVs like the first-gen Nissan Leaf look like a throwback to a very primitive time. A 2025 Mercedes EQS 450+ has an official WLTP range of an almost diesel-like 481 miles in its leggiest form. But that’s put in the shade by the car you see in these pictures, a Mercedes EQS prototype that recently drove 749 misty miles on a single charge. Having left Germany, crossed Denmark and arrived in Malmo, Sweden, the special EQS still had 85 miles left in the high-tech tank. The original Leaf was only good for about 99 on a charge.

To make a current lithium-ion EQS capable of covering 1205km (749 miles) on a charge you’d need to vastly increase the size of the already huge 118kWh battery. The result would be expensive, heavy, inefficient and also probably look like a funeral car due to the wheelbase stretch needed to slot the enlarged power pack under the floor. But solid-state batteries, as used in that prototype, are far more energy-dense and that’s why car makers are champing at the bit to get them to market and silence range-anxious EV naysayers once and for all.

You might be surprised to hear, given the benefits, that solid-state batteries aren’t really much different to the ones fitted to the EVs we can buy today. When we discharge a battery, ions flow from the negatively charged lithium cathode to the positively charged graphite anode, and in an existing lithium-ion pack the anode and cathode are separated by an electrolyte gel. In a solid-state battery that gel is replaced by a solid ceramic or polymer-based electrolyte, and the anode is usually made from lithium.

Helped by the solid electrolyte’s smaller size, Merc’s air-cooled solid-state battery, co-developed with the AMG F1 team and solid-state specialists Factorial Energy, has 25 per cent greater energy density than a regular liquid-cooled lithium-ion version. Some tech firms talk of doubling density, but whatever the gains it means more range for the same given footprint.

Though in theory that extra density could make it possible for car makers to deliver production EVs that hit that 749-mile benchmark (Toyota, in partnership with Panasonic, is aiming to do just that), in practice it means they’ll be able to build cars whose range matches or exceeds that of today’s cars – often in the region of 300-400 miles – but which weigh far less. And less weight means greater efficiency. It’s a virtuous circle.

Solid-state tech will also be key to allowing brands like Bentley to actually enter the EV space at all without serving up cars as grotesquely overweight as the 4100kg Hummer EV, or as compromised from a touring point of view as the electric Mercedes G-Class, which can barely manage 250 real-world miles between charges despite packing 116kWh of juice between its axles.

The benefits, though, go further than simply going further. Solid-state batteries can charge faster, potentially cutting the 30 minutes it takes the average modern EV to fill from 10 to 80 per cent (even the fastest 800-volt cars need around 16 minutes) to less than 10 minutes. They should also have a longer service life: think 5000 charge/discharge cycles and still going strong versus 1500 cycles.

Another major advantage is that solid-state batteries are less dangerous. We’ve all seen photos and video of EVs on fire. But solid-state batteries have a higher thermal stability and non-flammable, non-leakable electrolyte, massively reducing – though not totally eliminating – the dangers.

Mercedes is far from the only company banking on the breakthrough. BMW, Volkswagen and Stellantis are foremost among the Western car makers, and many Chinese manufacturers are working on incorporating it into future EVs.

How far into the future? BMW began testing a solid-state i7 earlier this year, and the 749-mile EQS brings us a step closer to showroom reality. But we probably won’t get the first solid-state production cars until the end of the decade. Mercedes suggests 2030 for its first such EV; Honda claims it’ll get there a year or two earlier.

Luxury and performance cars are likely to be the first in line due to the high cost of the fledgling tech, which requires more rare metals, and widespread adoption on mass-market EVs is not likely until well into the 2030s. Even then the takeover won’t be absolute. Although lithium-ion batteries remain the single most expensive part of any EV, the cost has come down dramatically in recent years due to the benefits of scale production, and that’s hard for car makers to ignore.

Other stumbling blocks include difficulties in producing them in large quantities and overcoming the formation of life-sapping dendrite structures on the anode during charging, something that was initially thought only to affect conventional lithium-ion batteries and not solid-state.

As a stepping stone some car makers, including MG, are fitting EVs with semi-solid-state batteries, in which a not-quite-solid gel electrolyte gives a taste of the future without the production pain. Think slightly longer lifespans and better energy density than current packs, but not solid-state-grade performance and still with some overheating worries.

And there remains potential for squeezing more miles from conventional batteries with some clever tinkering. BMW’s Neue Klasse iX3 and next year’s related NK 3-series are too early for solid-state power, but their innovative round cell design improves energy density, reduces charge times and cuts the CO2 footprint. The iX3 claims 500 miles of WLTP range, and 400kW charging allows it to add almost half that in 10 minutes.

In a similar vein Mercedes’ G-Class with EQ Technology is rumoured to be in line for a new type of battery chemistry that could give another 100 miles of range starting next year. And raining on Benz’s EQS parade and the entire solid-state buzz is the awkward news that a standard Lucid Air of the kind you can already buy in the US covered 749 miles on a big (112kWh) but ordinary lithium ion battery in July, earning itself a Guinness World Record in the process.

Mind you, it did start at St Moritz on the Alps, and finished in Munich, which is over 1300 metres closer to sea level, so had a major topographical advantage. A Citroën 2CV will probably do 100mph if you can find a steep enough hill.

Eventually, though, solid-state batteries will render that kind of dice-loading unnecessary, and today’s 100kWh-plus heavyweight batteries laughably obsolete, car makers tell us. They’re definitely still coming, we’re promised. Just not yet.