Solid-State Batteries: Status and Timelines

Every battery in an electric car or a home storage unit today works the same way at heart: it stores energy as chemical energy, which is converted back to electrical energy when the battery is discharged¹. Almost all of them are lithium-ion or lithium-ion polymer cells, built around a liquid electrolyte, an organic solvent that carries charge between the positive and negative electrodes². A solid-state battery is the same idea with one part swapped: the liquid electrolyte is replaced by a solid material.

That single change is why solid-state batteries attract so much attention, from car makers and from households watching the emerging home energy technology market. The promise is batteries that store more energy in the same space, charge faster and are safer, because the flammable liquid solvent is gone. The reality is that the batteries you can buy today, for a car or for a home, are not solid-state. This page sets out what the technology is, what it claims to offer, where it stands, and what today's batteries already achieve in the meantime.

Solid-state batteries explained: solid electrolytes replace liquid ones

The clearest way to understand a solid-state battery is to look at how the law defines the batteries we already have. The Lithium-ion Battery Safety Bill [HL] defines a lithium-ion battery as "a secondary (rechargeable) battery with an organic solvent electrolyte and positive and negative electrodes which utilize an intercalation compound in which lithium is stored"³. That organic solvent electrolyte is a liquid. It is what carries the lithium ions back and forth inside the cell as it charges and discharges, and it is also the part of the battery that can catch fire if the cell is damaged or overheats.

A solid-state cell keeps the electrodes and keeps the lithium, but replaces that liquid with a solid electrolyte: a ceramic, glass or similar material that conducts ions while remaining rigid. Nothing else about the basic principle changes. The battery still stores energy chemically and releases it as electricity on discharge¹. A battery storage system, in the general sense, is simply "a system that stores electricity, usually from renewable sources, for later use"², and that is as true of a solid-state cell as of any other.

The distinction matters for households because the rules that govern home storage are written around what a battery does, not what it is made of. UK legislation defines an electrical storage battery as equipment "intended for use solely for storing energy converted from electricity that was supplied to the residential accommodation or building in question, or generated by a microgeneration system"⁹. A solid-state home battery would fall under that same definition, and under the same VAT treatment, installation rules and standards as today's lithium-ion units. The technology would change what is inside the box, not the box's place in your home.

The case for solid-state: higher density, faster charging, improved safety

The case for solid-state batteries rests on three claims, and it is worth separating what drives each one.

The first is energy density. Most current EVs use lithium-ion or lithium-ion polymer batteries precisely because of the high energy density these chemistries achieve¹⁰. More energy in the same weight and volume means either a longer range from the same battery, or the same range from a smaller, cheaper battery. A solid electrolyte is one route to packing more energy into a cell, which is why vehicle makers are the loudest voices behind the technology.

The second is safety. The liquid organic solvent in a conventional lithium-ion cell is flammable, and battery safety has risen far enough up the UK agenda that a private member's bill has been introduced to define and regulate these batteries, including stand-alone grid-scale battery energy storage systems³. Removing the flammable liquid removes the main fuel for the kind of thermal runaway fires that have driven that regulatory attention. The safety claim is the most physically grounded of the three, though a solid cell still stores a large amount of energy and still needs proper protection in use.

The third is lifespan, and here the comparison with older chemistry is instructive. Lead-acid batteries, still common as a cheap storage option, typically provide around 700 to 1,000 charging cycles¹¹. A lithium-ion battery, by contrast, can typically handle around 4,000 charging cycles and last 10 years or more¹¹. Each generation of battery chemistry has delivered a step change in cycle life, and solid-state designs are claimed to continue that pattern, though no UK figure for solid-state cycle life exists yet to put beside these numbers.

Current progress: still being developed, unavailable to buy

The honest status report is that solid-state batteries are not a product a UK household can buy, for a car or for a home, and no verified production or on-sale date for the UK appears in any official or independent UK source. What can be stated firmly is the state of the market that solid-state would enter.

Home battery storage itself is established and growing. MCS, the certification body, has recorded domestic retrofit battery installations since September 2023, before which no data is available¹². The government's own modelling looks much further ahead: National Grid's Future Energy Scenarios forecast 1.5GW of small battery storage, domestic and commercial combined, around a third of total battery storage deployment capacity, by 2040¹³. That is the demand solid-state cells would eventually serve.

Two things are worth watching in the meantime. First, the safety framework is still being built. The Energy Safety Association has announced work "to help develop an evidence-based framework for the safe deployment of plug-in battery energy storage systems in UK homes"¹⁴, a sign that even today's plug-in products are ahead of their standards. Second, scale still matters: the National Energy System Operator notes that compared with pumped storage, the electricity batteries deliver "is much more limited"¹⁵, which is why grid-scale storage and household storage are different problems. A technology that raises energy density would ease both, which is part of why the timeline question attracts so much attention.

For a household weighing a purchase today, the practical reading is this: the technology readiness of solid-state cells sits well behind the lithium-ion and sodium-ion home batteries you can actually buy, and any date quoted for a solid-state product should be treated as a claim by its maker until the product appears with certification behind it.

EV batteries typically survive 10 to 20 years

While the next chemistry is developed, the current one has quietly become long-lived. EV batteries are expected to last 10 to 20 years⁴, and they can last for hundreds of thousands of miles, which is why EVs do not usually need their batteries replaced⁷.

That figure deserves unpacking, because "battery life" is often misunderstood as the point at which the battery stops working. It is not. A lithium-ion battery degrades gradually: each of its roughly 4,000 charging cycles takes a small toll, and after 10 years or more of use the battery still holds charge, just less of it than when new¹¹. A car that managed 250 miles per charge when new might manage somewhat less after a decade, and for most households that remains entirely usable.

The comparison with older storage chemistry shows how far this has come. Lead-acid batteries, the traditional cheap option, manage around 700 to 1,000 cycles before they are spent¹¹. A modern lithium-ion EV battery manages around 4,000¹¹. That is the standard solid-state designs will be measured against, and it is a high one: any new chemistry has to beat a battery that already outlasts most of the car around it.

Degradation is also not uniform. How a battery is treated, how often it is rapid charged, how low it is allowed to run and how hot it gets, all affect how quickly capacity is lost, which is why charging habits matter as much as chemistry. Those habits are covered further down this page.

Battery size and range: choosing between 230 and 450 miles

Battery capacity is the main driver of an EV's range, and the range figures on sale in the UK have climbed steadily. The average battery range across new models is now more than 230 miles⁶, some variants already on sale have maximum battery ranges in excess of 450 miles¹⁶, and larger passenger cars, which can accommodate larger battery packs, deliver ranges of over 250 miles².

The trade-off behind these numbers is simple: a bigger battery means more range, more weight, more cost and more raw materials. A smaller battery means the opposite, and for most daily driving, a smaller battery is enough. That is the calculation solid-state technology is trying to change. If a solid cell stores more energy per kilogram than a liquid one, the same range could come from a smaller, lighter battery, or a car could offer far more range without a heavier pack.

One practical note on reading range figures: the range a car actually delivers depends on its battery state of charge⁷, along with driving style, speed and temperature. A quoted maximum range is a best case, achieved with a full battery in favourable conditions, not a promise for every journey. Planning journeys so you know how far you will travel and how much charge you will need, and using chargepoint finder apps to map chargepoints along the route, is standard practice⁷.

Charging at home: roughly £17 a full charge, and the slowdown after 80%

Charging at home is where an EV is cheapest to run. A full charge at home for an electric car with a 50kWh battery capacity costs approximately £17 on a standard tariff⁴. Charging overnight, when many tariffs are cheaper, brings the cost down further, and the running-cost advantage over a petrol or diesel car is real: one typical charging pattern, 80% at home and 20% on rapid public points, showed a £450 annual saving², while a heavier public-charging mix, 50% home, 25% slow public and 25% rapid, cost around £1,100 a year at 10,000 miles¹⁷.

Getting a charge point installed is a separate cost. A typical domestic installation is worth £800 to £1,500 for the electrical work, excluding the charger unit⁸. Smart charging capability is a legal requirement for charge points sold in the UK, not an optional extra⁸.

Charging speeds at home are modest compared with public rapid points. Fast chargers usually take between four and eight hours to charge an EV battery¹⁸, a slow charger will normally fully charge a partly charged car in around four hours¹⁹, and low-power charging can take anywhere from six to 18 hours to reach 80%²⁰. On the public network, rapid and ultra-fast points can charge 80% of an EV battery in 30 to 60 minutes¹⁹, and a rapid or ultra-rapid charge from 20% to 80% should be allowed at around 40 minutes²¹.

The 80% figure recurs for a reason. Charging slows significantly after about 80% to protect the battery and prolong its lifespan, so charging up to 80% is generally recommended²². The rate of charge slows as the battery approaches 100%, and also at lower states of charge, for example below 10%⁵. In some cases it can take as long to charge from 80% to 100% as it does from 20% to 80%²⁰. As a rule of thumb, charging an EV from 20% to 80% should take between 30 and 90 minutes on a rapid point²². Rapid and ultra-rapid chargers safeguard battery life by slowing charging once the battery reaches 80%¹⁸.

Charging routines that keep a battery healthy

Chemistry sets the ceiling on battery life; habits determine how close a battery gets to it. The guidance is consistent across independent sources.

• Only use rapid charging when you need to, and rely on slower charging for routine top-ups⁷.
• Do not fully charge the battery as a matter of habit, and do not let it get too low on charge⁷.
• A good rule of thumb is to avoid letting the battery fall to the 20% mark²³.
• Charge overnight so that you start each day with a full battery⁷.
• The ideal temperature for an EV battery to charge is around 25 degrees Celsius⁵.

None of these are rules with penalties attached; they are habits that reduce the wear each cycle causes. A battery that is routinely rapid charged from near-empty to full will degrade faster than one kept in a comfortable middle band and charged slowly at home, but both will still work for years. The habits matter most for households planning to keep a car long-term, or planning to use the battery hard through bidirectional charging, where every cycle counts against the warranty terms discussed below.

Cover and lifespan: eight years or 100,000 miles

The warranty is the figure a buyer can hold onto. Manufacturers provide warranties on EV batteries lasting at least eight years or 100,000 miles²⁴, and most electric car batteries are guaranteed by manufacturers to last for eight years or around 100,000 miles²³. Which?'s EV reliability survey found that EV battery warranties usually last eight years, and there is no evidence yet that this is the ultimate lifespan of a battery²¹.

Set against the expected life of 10 to 20 years⁴ and the roughly 4,000 cycles a lithium-ion battery can typically deliver¹¹, the warranty looks conservative, and that is deliberate. A guarantee has to cover the worst-treated battery in the fleet, not the average one. A battery that reaches the end of its warranty with most of its capacity intact has years of service left, and the second-hand EV market increasingly prices cars on measured battery health rather than age alone. Batteries that do fail can usually be replaced, though it is complicated and often expensive to do⁷, and retired EV batteries are increasingly finding a second life in home storage, a route covered on our second-life EV batteries page.

For households using the car's battery to serve the grid, warranty terms matter even more. Vehicle-to-grid operation adds cycles, and whether that voids the battery warranty depends on the manufacturer's own conditions, a question examined in detail on our page on V2G, battery degradation and vehicle warranties.

Using an EV battery to hold your solar electricity

Yes, solar panels can charge an electric car, though you are unlikely to rely entirely on solar power year-round in the UK, especially in winter²⁵. The more interesting question is whether the car's battery can hold the solar electricity your home does not use, and here the current answer is: not directly, in most homes.

With solar panels alone you cannot store leftover energy for later; a battery can store energy you have not used²⁶. The electricity a solar PV system generates can be used throughout your home, exported to the grid, or stored in a battery for use at another time²⁷. Home storage batteries store your electricity to use later, making your energy system more independent from the National Grid²⁸. Without a home battery, surplus solar electricity is wasted or exported to the grid, often at a relatively low rate; with one, that surplus is captured and held for when you actually need it, including overnight EV charging²⁵.

The technology that would let the car's own battery do this work, vehicle-to-home and vehicle-to-load charging, is emerging in the UK but is not yet the norm, so most solar households buy a separate battery. Combining rooftop solar with a battery could enable 80% of a household's annual electricity to be low-carbon²⁹, and any electricity you still export can earn money under the Smart Export Guarantee, in which all licensed electricity suppliers are required to participate in declaring their status on an annual basis³⁰.

Solid-state's potential impact on energy independence at home

More homegrown energy means greater energy independence³¹, and batteries are the piece that makes homegrown energy useful after the sun goes down. A solid-state battery, if it arrives at the promised density and lifespan, would sharpen that equation in three ways: more stored energy per pound spent on the battery, more cycles over a longer life, and a lower fire risk sitting on a garage wall.

The dependence that remains is worth stating plainly. A household with solar, a battery and an EV still depends on the grid for the electricity its panels do not generate, on a supplier for the tariff that prices what it imports and pays for what it exports, and on the manufacturer of the battery and the car for warranty, spare parts and software. A better battery reduces the quantity of that dependence, not its existence.

The timeline, as far as it can be stated, is that solid-state remains a development while the installed base grows around it: MCS has recorded domestic battery installations only since September 2023¹², the government's scenario work sees small battery storage reaching 1.5GW by 2040¹³, and the safety framework for even plug-in home batteries is still being written¹⁴. On the vehicle side, a Battery Passport will be required for specified EV batteries placed on the EU market from February 2027, with full compliance from 18 February 2027, a marker of how tightly documented battery supply chains are becoming. For a household deciding today, the sound position is to buy the storage that exists, size it for the solar you have, and treat solid-state as the upgrade path rather than the reason to wait.