Does your car suffer 'vampire drain'?!

I’d not previously come across the fabulous phrase - ‘vampire drain.’ It describes the scenario when a car battery (or indeed any battery appliance) reduces in strength even when not being driven/used. The culprits apparently are all the electronics churning away in the background, eg items on standby mode, clocks, back ups etc.

I noticed it with our ‘new’ 2nd hand EV (Renault Zoe) where we seem to lose about 5% charge overnight, when unused. Apparently it can apply to many cars, but the loss of battery strength is all too apparent in an EV!

Has anyone come across any simple (I’m not a car/technical person!) means of reducing the vampire drain in an EV, or is this just one of those things you have to live with?

The car I just restored to get back on the road recently had exactly this problem. I would charge the battery, leave it a couple of days then it would be flat enough to not start. A tad frustrating, but then I looked up battery drain on youtube and found the answer.

It’s a little laborious but essentially you connect a voltmeter set to measure milliamps between the battery negative terminal and negative lead. The meter will show a number of milliamps on the display which is what is currently being consumed. If the reading is too high (think it’s above 85 milliamps for new fossil fuel cars), then you have parasitic draw. Not sure what the ‘normal’ draw is for an EV but you can google it.

To then identify where the draw is coming from, you simply go through the car fuseboard removing and replacing fuses until you see an abnormal drop on the voltmeter display. In my case I had a faulty alarm and ignition switch. Changed both and all was well😁


Think this was the vid I used.

Our radio was a vampire, running the battery down to the point of not starting after about 3 days of non use.

Well if you will insist on a 300 watt sound system with 500 watt sub-woofers… :rofl:


I’ve a few cars that sit around, from a Morgan with a battery isolation switch to a C350 hybrid that will sit for a year and still start. All batteries will loose charge over time and most cars, EV or ICE, have a drain on the battery even when “turned off”. I think the term “vampire” is a bit strange because it is the car drawing the charge not some bat like creature hovering above :face_with_hand_over_mouth:

There are two solutions to battery drain, plug the battery into a charger or isolate the battery (it’ll still drain but more slowly).

I think the link is to one of these “teaching your grandmother to suck eggs” blogs/videos. No offense intended :slightly_smiling_face: just a friendly observation.

Has anybody else experienced the frustration of searching for a simple solution to a simple problem and ended up with some twit making a Cecil B. DeMille Youtube production on replacing a screw?

Update: A no shit Sherlock moment @letsmile after watching (with the odd fast forward) the diagnoses that leaving the interior light on caused a draw on the battery. FFS.

Think you may have totally missed the point on parasitic draw. This isn’t simply leaving a ‘normally operating car’ unused for a long period of time and the battery draining, which I think the majority of folks understand thanks. This is about abnormal drain on the battery leading to returning to a car after, in my case, a couple of days and it not being able to start. I personally don’t wish to have to recharge the battery every couple of days, or disconnect the battery, or put on trickle charge permanently.

No offense intended, but the devil’s in the detail, and understanding real solutions to real problems :wink::wink:

I suspect there aren’t many EV owners on the site, as yet… so perhaps you could also ask your question on an EV forum…

My 2006 car does have a duff-battery after a few days of non-use, due to the multitude of checks/whistles it has permanently on the go…
I leave it on trickle-charge/battery-tender whenever I kiss it goodnight… (unless I know I’ll be using it the next day)

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No worries Let’s, I understand the difference, but being an old “problem determination” sort of dude, I didn’t think the palaver the video went through was warranted, and the denouement of a light switched left on was somewhat of an anticlimax :face_with_hand_over_mouth: I hope you’ll forgive my joke :slightly_smiling_face:

I had a bloody rongeur munch through a high voltage cable on the hybrid just before be were off on a long trip last December. I’ve a much greater fear of rongeurs than vampires (or parasites’).

Wow - the battery shouldn’t be draining so rapidly. All cars have various levels of activity that continues after they’re locked, but there is a ‘normal’ limit on the draw. If your battery’s draining so quickly might be worth checking the battery condition or if you also have something abnormal causing the drain. Pretty simple to solve, and saves an awful lot of hassle. And imagine if you couldn’t hook it up to a charger away from home.

It’s OK… it’s just one of those things… which seems typical for this car… other owners tell the same story.
If I’m away from home, I’m using the car…

As I said earlier we had similar to Stella, Max 3 days and drained. The radio was doing it even though it was ‘off’ DH did some rewiring of it somehow and problem went away!

Indeed, and that’s exactly what I had, battery draining after a couple of days, then fixed the issue and now can happily leave the car days and days without any issues, and maybe even weeks.

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I had this on my Skoda Octavia diesel. In my case it was a corroded earth strap causing it. My mechanic said it was preventing the battery charging efficiently when I was driving. So not the vampire drain so much as a battery that couldn’t cope.

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Modern vehicles have all sorts of things that drain the batteries - alarm systems, clocks, the radio, even an internet connection in some cases!

A beefy diesel with stop-start might have a 100Ah battery - that will last 100 hours (just over 4 days) with a 1A load - but no-one really wants their battery to go flat after 4 days on the drive - I’d say a month would just about be the limit of acceptability, with enough juice left to start it - say 80-100mA absolute maximum when the ignition is off.

The easiest way to measure the current is with a clamp meter, as there is no need to remove the battery connections and risk car/radio settings being lost - but you need one with a low current scale such as the UNI-T UT210Eètres-Testeur-Capacitance/dp/B00O1Q2HOQ



Heck yes, @George1, even with a petrol car. The effect was different: in our case, it started showing I needed to drive it to charge it, but then it needed a new battery after 3 years.

I’m sure it’s worse with an EV.


Because there’s more “clever stuff” going on all the time? Because the batteries are designed to last much longer?

Tbh, I don’t know very much at all about it, so if the opposite is true, I’d be interested to learn more.

An EV is relatively unlikely to suffer much with vampire drain because the battery capacity is so much enormously larger.

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I also realised my (edited) answer was nonsense!