Storing an Electric Car: State of Charge and Long Lay-Ups

Storing an electric car is a newer question than it looks. The first wave of UK electric cars is now old enough to be a second car, a weekend car, or a car waiting for a decision.

Almost everything written about laying a car up assumes a fuel tank and a lead-acid battery. An EV has neither problem and two of its own.

Here is what actually matters: the state of charge, the 12 volt battery nobody thinks about, and what the car does while it thinks you have gone.

Storing an Electric Car Starts With State of Charge

A lithium-ion traction battery is happiest around the middle of its range. Manufacturers vary, but 50% to 60% is the consensus for a long stand, and most handbooks say something close to it.

Left at 100%, the cells sit at high voltage for months, which accelerates calendar ageing. Left near empty, the pack risks drifting low enough to trigger protection, and a pack that has gone into deep discharge can be an expensive recovery.

So the first rule of storing an electric car is unglamorous: charge it to about 60%, then stop. Do not leave it plugged in and full, and do not leave it on 8% because it happened to come home that way.

The Part That Actually Fails Is the 12 Volt

Almost every EV still has a conventional 12 volt battery, and it runs the things that wake the car up: the locks, the alarm, the modules, the screen.

On most cars it is small, cheap, and the first thing to die. When it does, the car often cannot be woken at all, because the contactors that connect the traction pack are themselves 12 volt devices.

That is the scenario owners do not expect: a full traction battery and a car that will not open. On several models the recovery involves accessing the 12 volt terminals through a panel, which is a lot easier in a workshop than on a driveway.

A conditioner on the 12 volt battery prevents the whole situation. It is the same add-on we fit to petrol cars and it matters more here, not less.

Vampire Drain Is Real, and It Varies Enormously

A modern EV never fully sleeps. Telematics, app connectivity, scheduled preconditioning and over-the-air updates all wake the car, and each wake costs energy.

Real-world drain ranges from well under a percent a week on a car that is left alone to several percent on one that is being polled by an app, sitting in a cold building, and updating itself.

Two practical steps help. Turn off scheduled preconditioning and any always-on connectivity you do not need, and keep the keys well away from the vehicle so it is not repeatedly detecting an approach.

Cold, Damp and the Rest of the Car

Everything that is not the drivetrain behaves like any other modern car. Brake discs corrode and pads bond over a few months, which on an EV is worse rather than better because regenerative braking means the discs were already lightly used.

Tyres flat-spot, and EVs are heavy, so they flat-spot readily. Raised pressures and a flat floor both help.

Damp affects an EV cabin exactly as it affects any other, so managed air is worth the same to it. A cold unheated unit also means the pack sits cold, and while cold storage is not harmful in itself, a frozen pack cannot accept a charge on collection day.

Should It Be Left Plugged In?

For a short stay, and if the car offers a charge limit, leaving it connected with a 60% cap is a reasonable arrangement. The car keeps its own 12 volt battery topped and manages the pack itself.

For a long stay in a building with no dedicated supply, storing an electric car plugged in is neither practical nor necessary. Charge to 60%, unplug, and put a conditioner on the 12 volt.

What is not sensible is leaving an EV plugged into a domestic socket on an extension lead for months in an unattended building. That is a fire risk rather than a charging strategy.

Keep the Paperwork Current

Electric cars are no longer exempt from vehicle tax in the UK, and owners who have never paid it are the ones most likely to miss the change. The current rules are on gov.uk.

If the car is off the road for the stay, a SORN stops the tax running and refunds full months already paid. The MOT still applies on the same schedule as any other car.

What It Costs

Secure indoor storage is £150 a month including VAT for the first three months, then £165. The humidity-controlled bay is £200, then £225. Minimum stay is one month.

A 12 volt battery conditioner is available as an add-on and is the single thing we would recommend for an EV. Figures sit on the locations and pricing page, and longer stays on the long-term car storage page.

How Pitstop 66 Can Help

Every car goes through the same eight-stage intake, gets photographed on arrival, and is looked at by a person every working day. An EV gets the same, plus a note of the state of charge it arrived at.

Mechanics are on site, and collection runs to 65 miles from Stalybridge by arrangement, which matters for a car that is off the road. Detail sits on the professional car storage page.

Owners reach us easily from Trafford and Salford. To arrange storage for an electric or hybrid car, enquire here or call 0161 464 7494.

Also worth reading: what changes after the first twelve months, why brakes seize after a lay-up and which storage tier a car actually needs.

Key Takeaways

• Charge to around 60% and stop. Not full, not empty.
• The 12 volt battery is what fails, and a dead one can mean a car that will not open.
• Turn off preconditioning and app connectivity, and keep the keys away from the car.
• Discs corrode faster on an EV because regenerative braking leaves them lightly used.
• Do not leave an EV charging on an extension lead in an unattended building.