Do electric cars lose charge when parked?

Jesse Crosse

29 Feb 2024

Do electric cars lose their charge if left unused for a long time? The answer to that is yes, but it can be as little as 1% per month depending on the car and the circumstances such as outside temperature. Assuming the battery is left in a reasonable state of charge, there should be nothing to worry about. 

Every electric car has more than one battery. The first is the powerful, high-voltage lithium ion battery that stores the energy to drive the electric drive motor. The second is the same kind of 12-volt battery that petrol and diesel cars have to power electrical equipment such as lights, instruments, audio system, horn and all the other ancillaries. Lithium ion batteries are found in lots of everyday things including mobile phones, tablets and laptops, but electric car high-voltage batteries are of the highest quality because of the scale of the job they have to do. They’re also extremely robust and not the delicate things some people imagine them to be. 

Background features draw power from the battery

When any car is turned off the electrical systems are still awake, readying it to respond to the remote key or keyless entry, perhaps powering an alarm or in an EV, providing the power to start scheduled charging or climate controls. The 12-volt battery in a petrol or diesel car is charged by the generator when the engine is running. 

An EV 12-volt battery is charged by the high-voltage lithium ion battery, so if the car is left standing and the voltage of the 12-volt battery drops while powering these behind-the-scenes electrical systems, then a relatively small amount of power will be drawn from the high voltage battery to keep it topped-up. People call this background use of energy “vampire loss,” or in engineer-speak, “parasitic loss.” Self-discharge for no apparent reason is imperceptible in a healthy high-voltage battery.

How should you prepare your electric car? 

So how should you prepare your EV for storage or a period of inactivity? For battery health reasons, manufacturers recommend you don’t charge an EV to 100% before leaving it standing for an extended period and neither should you leave it with the battery state of charge below 20%. The ideal is to leave the car when you take off on holiday with the battery state of charge at around 50% to 80%. Renault, for example, recommends that when storing Zoe for any period of time, charge the battery to 50% first. Also remember to turn-off any cabin pre-conditioning features, especially if the car isn’t being left connected to a charger.

Should I connect to a charger?

If leaving or storing your EV for a while at home or where it can be connected to a charger, then you have the option of setting a scheduled charge and also  the maximum state of charge to avoid it rising above a certain level. It’s worth bearing in mind that the question of leaving your electric car for weeks or maybe a couple of months is often only raised because it’s an electric car. Few people worry about leaving a petrol or diesel car when the fly off on holiday, yet because the engine isn’t running to keep the battery topped up, it’s potentially more susceptible to the 12-volt battery losing charge, especially during winter months. 

Electrical systems such as keyless entry and alarms are powered by the 12-volt battery

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