Almost every guide to car storage was written for a car with a carburettor and a key. Modern performance cars break several of those rules, and two pieces of advice that are still repeated everywhere are now contradicted by the companies that make the parts.
This is what actually changes when the car has software, a high voltage battery, carbon ceramic brakes and a particulate filter, and what a secure car storage facility should be doing about it. It applies as much to a modern GT or a fast estate as it does to a supercar.
Four things. The car never fully sleeps, so it drains itself. The brakes do not rust but can still seize. The tyres take a set faster than older ones did. And the engine needs a proper run rather than a warm up, because the exhaust filter only cleans itself under conditions that idling never creates.
None of that makes a modern car harder to store. It makes supercar storage a different job from classic car storage, and most of the difference sits in the electrical system rather than the mechanical one.
Because there are two batteries and the small one runs everything. The 12 volt battery powers the locks, the body electronics and the relays that connect the main battery to the car. If it goes flat, those relays cannot be told to close, so the car will not move no matter how full the traction battery is. On some cars the doors will not open either.
This is the single most common way a stored modern car becomes an immovable object, and it catches out hybrid and electric owners in particular, who reasonably assume that a healthy main battery means a healthy car. It does not. The 12 volt battery is the ignition key for everything else.
Weeks rather than months. A modern car with an alarm, telematics and keyless entry draws a small current continuously even when locked and asleep. Specialists working on one performance marque put a healthy resting draw at 20 to 50 milliamps and reckon on three to four weeks of standing before there is not enough charge left to start.
The arithmetic is worth understanding, because it explains why the answer is a conditioner rather than a bigger battery. A 70 to 80 amp hour battery is comfortably usable down to about half its capacity before starting becomes marginal, which leaves roughly 35 to 40 amp hours of headroom. At 30 milliamps that is about seven weeks. At 80 milliamps it is under three. Cold weather, an older battery, or one module that fails to go to sleep, and the number falls further.
The threshold that matters is 12.35 volts. Below that, according to battery manufacturers, the battery needs recharging immediately, because what follows is sulfation, and sulfation is permanent lost capacity rather than a flat battery you can simply top up. A stored car that is checked weekly and kept on a conditioner never gets near it.
Whatever the handbook says, and there is no single right answer. Published guidance ranges from 20% to a full charge depending on the manufacturer. Tesla say around 50% and plugged in where possible. Porsche say 20 to 50% for a general layup, but their own petrol electric 911 tells owners never to let it below 30% and to charge above 80% before parking for two months.
The reason the numbers vary is that they are all managing the same trade off from different starting points. A lithium battery ages while it sits, not only while it is used, and the rate at which it ages depends on how full it is and how warm it is. A fuller battery ages faster. So does a warm one. That is why almost every manufacturer that publishes a figure also publishes a temperature range, and why a cool building matters more for a modern hybrid than it ever did for a carburettor car.
What none of them recommend is leaving it flat. A Tesla will lose roughly 1% a day sitting still, which is around 14% over a fortnight, and letting the pack reach zero can damage other components.
Away from the car, with a fresh cell in it, and ideally in the manufacturer’s key saving mode if there is one. Toyota, for example, publish a battery saving function that stops the key listening for the car at all. The drain that is actually documented is on the key rather than on the car.
The advice you will read online is to keep the fob a specific distance away, usually quoted as fifteen or twenty feet. We could not find a single manufacturer publishing that figure, or any manufacturer statement that fob proximity meaningfully drains the vehicle. Whether the car listens continuously while asleep depends on how the system was designed. Storing the key separately is still worth doing, for the key’s own battery and to remove any relay theft opportunity, but it is not the fix for a flat car.
Yes, and this is where the popular advice is most wrong. The ceramic disc face genuinely does not rust. But the pad can still bond to the disc after long standing in damp air, and the steel bobbins that join the ceramic ring to its hub still corrode. The disc being rust proof does not make the brake rust proof.
The evidence here is unusually good, because it comes from the company that makes the disc material. SGL Carbon hold a patent on parking brake designs for carbon ceramic discs, and the patent exists precisely because, in their words, an interlayer forms between disc and pad after a long standing time, particularly in moist surroundings, through corrosion at the contact surface. The corrosion comes from the metal content of the pad and from material transferred onto the disc, not from the ceramic. The seizure it produces is the same as on an iron brake, and the consequence is worse: freeing a bonded pad can tear the silicon carbide friction layer, and that layer cannot be machined back.
Two other things go wrong that nobody mentions. The steel floaters connecting the ceramic ring to the aluminium hub can seize with corrosion, which stops the ring expanding freely under heat and cracks it. And the pads are still steel backed, so corrosion at the bond between friction material and backing plate can delaminate the pad.
So the old instruction to cycle the brakes before storage to clear surface rust does not apply to the disc face. Drying the brakes with a short drive before the car goes away still applies, for the calipers, the hardware and the pads.
No, and on a carbon ceramic car the reason is stronger than on an iron one. The pad and disc bonding described above happens at the interface held under clamp load, which is exactly what an applied parking brake creates. Leave it off, chock the wheels, and check the handbook for how the electric parking brake behaves when the car is left in park.
Some cars apply the parking brake automatically when you select park or switch off, and that function may need disabling for storage. It varies enough between models that it is worth checking rather than assuming, and it is the sort of thing a facility that stores modern cars should already know for your car.
Michelin say no. They state that over inflating will not prevent flat spotting and in some cases can make it worse, and recommend keeping tyres at the pressure on the car’s own placard and no higher. Continental disagree mildly and suggest around 3 PSI above normal, never above the maximum cold pressure marked on the tyre.
This is a genuine split between two tyre manufacturers rather than a settled fact, and we are flagging it as one. It matters here because Michelin supply original equipment to most of the performance car market, and because pumping storage tyres to 40 PSI is close to universal practice.
What both companies agree on is the actual answer: take the load off. Michelin say that where a vehicle is parked for a long period the weight needs to be taken off the tyres, using stands or dedicated tyre cradles, and that failing to do so may cause irreversible damage. That is the method with no dispute attached to it.
Yes, measurably, and for three reasons that compound. High speed rated tyres use a nylon reinforcement that takes a set when held flat. Low profile sidewalls cannot flex the deformation away, so the load goes into the footprint. And modern cars are heavier, so the load per contact patch is higher.
Continental put the line between temporary and permanent at around a month. Under that, a flat spot generally disappears once the tyres reach proper operating temperature, and Michelin note that the vibration usually settles after twenty minutes or so at motorway speed. Standing under load for a month or longer causes the kind of set that normal driving will not remove.
Which is why moving the car matters more on a modern car than it did on an older one, and why a car storage facility that moves stored cars on a stated interval is worth more than one that does not.
The car settles, and the compressor may keep trying to hold it up. Air springs are rubber bellows that develop small cracks with age, and a car that drops overnight is leaking. A leaking system makes the compressor run repeatedly or continuously, which drains the 12 volt battery and can overheat the compressor.
We should be honest that this is an inference from suspension service literature rather than something manufacturers publish. We checked the handbooks for several cars with air suspension and none of them contains storage guidance at all. What is manufacturer stated is that some cars self level even with the power off, which means the system can wake and run while the car is in storage, and that lifting such a car onto stands generally requires putting it into a jacking mode first so the levelling does not fight you.
Fill the tank almost full and use super unleaded. Standard 95 octane petrol in Great Britain has been E10 since September 2021, meaning up to 10% ethanol, and ethanol draws water out of humid air. Super unleaded is still sold as E5, with no more than 5%. A nearly full tank leaves little air space for moisture to condense in.
Note that E5 is not ethanol free, it is a lower limit. And the risk most often described, water separating out at the bottom of the tank, is not the one that usually bites. Research for the United States Department of Energy found that petrol loses its lighter, more volatile fractions within about six to eight weeks, well before separation becomes the operative problem. A car that will not start after a long layup is far more often suffering from stale fuel than from water.
Less than the marketing suggests. Testing funded by the United States Department of Energy found untreated petrol still met its specification after twelve months of ageing without any aftermarket additive. For a single winter, stabiliser is optional. For a car going away for more than a year, it earns its place.
The instruction that matters more is one nobody sells: do not drain the fuel system. The Federation of British Historic Vehicle Clubs advise against leaving it dry, because gaskets and elastomers shrink and crack as they dry out, and an empty tank corrodes internally. If you do add stabiliser, run the engine afterwards so treated fuel reaches the injectors rather than sitting in the tank alone.
Not for a few minutes on the drive, no. On a modern petrol car with a particulate filter, a short idle actively makes things worse. It adds soot to the filter, puts condensation into the exhaust and the oil, and never reaches the conditions under which the filter cleans itself.
A petrol particulate filter cleans itself opportunistically, mostly during deceleration with the throttle closed, when no fuel is being injected and the engine is pumping air through an already hot filter. That combination, heat plus oxygen, is what oxidises the soot. Idling delivers neither. A diesel filter is more demanding still: passive cleaning needs exhaust temperatures around 275 degrees and above, and active cleaning targets around 600 degrees, neither of which happens on a driveway.
Worth knowing, because it is a real contradiction rather than a straw man: at least one manufacturer press office has advised starting a plug in hybrid weekly for fifteen minutes to look after the 12 volt battery. That advice solves the battery problem and creates the filter problem. The resolution is to use a mains conditioner for the battery and a proper drive, warm through, for everything else.
Put the car away completely dry. The film manufacturers publish no guidance about covers or storage at all, but they are explicit that water should never be left to evaporate on a coated surface, because tap water carries minerals that leave deposits. On a hard coating those deposits are difficult to remove without taking the coating with them.
You will read that non breathable covers trap condensation and damage film. That may well be true, but we could not find a manufacturer, a testing body or any published work supporting it, only companies selling covers. What is documented is the drying instruction, which is why a facility that air dries a car for a day before covering it is doing something that matters rather than something ceremonial.
Only downstream of the battery. Connected cars keep drawing power in storage, and over the air updates need a minimum state of charge before they will install. So a car that has been sitting will stop updating, but the cause is the charge level, not the updates. Keep the car powered and they look after themselves.
The practical consequence is at the other end. A car that has been away for months will have a queue of updates waiting, and they need charge and time to install. That is worth doing before the car goes back to its owner rather than in their driveway.
Twelve jobs, and which of them a car storage facility should be doing rather than you. The ones marked as varying are the questions worth asking before the car arrives, because that is where operators differ most.
Three questions separate the operators who understand a modern car from the ones storing it the way they stored a Jaguar in 1995. Do you run the engine to full operating temperature or just start it? How often is the car moved? And what do you do about the high voltage battery?
The first question is the most revealing. Running to operating temperature and idling for ten minutes are described in almost the same words and are not remotely the same thing. The second matters more than it used to, for the tyre reasons above. The third is the one most prestige car storage operators have no answer to at all, because their process was written before any of their customers arrived in a hybrid.
Henry’s Car Barn has provided secure car storage since 1984, from sites in Warwickshire, Hampshire, West Sussex, London and Northumberland. The fleet runs from pre war machinery to current hypercars, so the process has had to keep up rather than stay where it was.
Every car is inspected on arrival, air dried for twenty four hours, photographed before it goes into its bay, and put away with the handbrake off, a breathable cover, a battery conditioner and a drip tray. The site is inspected daily, conditioners are checked weekly, and roughly every sixty days each car is uncovered, started, run up to full operating temperature and moved so the tyres do not sit on the same patch. Pennant Classics, our workshop, is on the Warwickshire site, which means anything the car needs can happen without it being transported anywhere.
If you would like to talk through what car storage would involve for your car, classic or modern, get in touch and we will walk you through it honestly, including the parts you could perfectly well do yourself.
