Vampire drain, ghostly quiet and scary sums: an electric car Halloween special

The pumpkins are out, the evenings are drawing in and it'll soon be pitch black by teatime. It's spooky season, and drivers get a few frights of their own.

Does an electric car quietly lose charge while it sits on the drive? A little, but not enough to haunt you. 

Why do electric cars hum at low speed? It's a safety feature, and it matters more than ever with trick or treaters around. 

And what does a tank of petrol cost this October half-term? You might want to sit down for that one.

Yes, a little. An electric car parked up slowly loses some charge, because a few of its systems stay awake while you sleep. We’ve called it vampire drain. Engineers prefer "parasitic loss", which is somehow even creepier.

The good news is that it's usually only a tiny amount. Electrifying.com says it can be as little as 1% per month, depending on the car and conditions such as the outside temperature. For most drivers doing everyday journeys, you'd barely notice.

Picture your car as a vampire resting in its coffin. It's asleep, but a few things keep ticking over in the background:

• the alarm and keyless entry, so the car knows when you're coming
• apps and connected services checking in
• software updates downloading overnight
• camera security modes, if your car has them
• the car warming or cooling its own battery when it's very cold or very hot

The real monster in the closet is often the small 12-volt battery. It runs the locks, lights and alarm, and the big battery tops it up when it gets low. If it goes flat, the car may not wake up, even with plenty of charge in the main battery. So it's the one to keep an eye on if you're leaving the car for a few weeks.

1. Switch off what you don't need. Camera security modes and remote climate control are handy, but they keep the car awake.
2. Don't leave your battery full to the brim or running on empty. For longer spells parked up, Renault recommends charging to between 20% and 50%. Other car makers give different advice, so check your handbook.
3. Stop checking the app every hour. Every peek wakes the car up. Let it rest in peace.
4. Plug in if you can. Leave it connected at home with a charge limit set, and it'll top itself up when it needs to.
5. Going away? Park somewhere sheltered if you can, and follow the manufacturer’s advice for leaving it.

Worried about how long the battery itself will last? Our guide to electric car batteries has the answers.

Electric cars are so quiet at low speed that they come with a sound generator, so people on foot can hear them coming. It's called an Acoustic Vehicle Alerting System, or AVAS. So yes, that gentle spooky hum you hear from an electric car in a car park is a "fake" noise, added on purpose.

Petrol and diesel cars announce themselves with engine noise. Electric cars don't have much to say at low speed, so AVAS fills the silence. Under the UK regulations, it plays a sound from the moment the car pulls away up to about 20km/h (roughly 12mph), and whenever it's reversing. Above that speed, tyre and wind noise do the job instead.

The sound became compulsory on new types of electric and hybrid cars from 1st July 2019, and on all new ones registered from 1st July 2021, according to the RNIB. Older electric cars may not have one, which is worth knowing if you're driving one.

Can drivers switch it off? In March 2024, the RNIB reported that the Department for Transport had confirmed a ban on pausing the sound in new electric cars registered from 1st September 2023.

Car makers can choose their own sound within the rules, so no two ghosts in the machine sound quite the same.

This year the clocks will go back on Sunday 25th October, the October half-term will follow, and Halloween is on a Saturday. That adds up to a lot of excited children out after dark, often in dark costumes, with masks that can block their view of the road.

Halloween is one of the riskiest evenings of the year for children on foot. A 2021 study of UK data found more child casualties between 5pm and 7pm on Halloween than on other days, including public holidays.

Whatever you drive, a few simple habits help:

• Slow right down on residential streets in the early evening.
• Expect children to step out from between parked cars.
• Take extra care pulling in and out of driveways.
• Keep your headlights dipped so you don't dazzle anyone crossing.
• Remember that AVAS only works at low speed. Being heard isn't the same as being seen.

If you drive a petrol car, the fuel gauge might be the scariest thing you see all month. According to the RAC, unleaded averaged £1.74 a litre on 30th September 2026. That's 41p more than at the start of the US/Iran conflict, and it takes the cost of filling a family car to nearly £96. Diesel drivers are having an even worse time, with prices reaching a record £1.99 a litre on the same day.

So how do the sums look in an electric car you charge at home? A full charge at home can cost just £4.07 in a typical EV, compared with £38.79 for the same amount of miles in an equivalent petrol car.

Put another way, you can charge at home for as little as 2p per mile, with an exclusive EV charging tariff from Octopus Energy, compared with 18p per mile for petrol. Over a year, that's as little as £148 to charge at home, compared with £1,411 for petrol.

That tariff is Octopus Energy's Intelligent Octopus Go - EV Saver, and it's exclusive to Octopus EV drivers. Octopus EV drivers get an exclusive 1p discount on the fixed rate with Intelligent Octopus Go - EV Saver. That means charging at home for just 6.6p per kWh. Turns out the witching hour is the cheapest time to charge.

So this half-term, the only fright in an electric car should be the mountain of sweet wrappers in the footwell. Happy Halloween!