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My car (2014 Opel Zafira-B) has some weird electrical issues where it randomly and suddenly drains the battery, sometimes while driving. While diagnosing the issue I also measured the power drain when the car is "off". (Of course it's never really off, it's constantly listening for the keyfob for example.)

After I locked the car the power drain is still about 1 A for a few minutes and even after 10 minutes of leaving the car alone it's still a couple hundred milliamps.

Now automotive isn't really my area of expertise but embedded systems design somewhat is and I find this quite a lot for a battery powered system, hence my question:

What's the typical power consumption of a parked car? And how long does it usually take until all control units reached their final sleep state?

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    We might be able to answer this for your Opel, but there's no definitive answer for every car out there ... well, at least there isn't a common answer here. Every automaker out there can set whatever time they want to for any given model. Then, it also depends on user settings, take for instance a Tesla. If the owner has some security options set, you'll never get to that state because it is always polling the environment it's sitting in to see if anything is around it.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Feb 15 at 22:51
  • @Pᴀᴜʟsᴛᴇʀ2 Yeah, I'd exclude electric cars, but since regular cars of a particular period all have similar battery capacities I'd assume they also have similar expectation w.r.t. how long they can be parked without the battery going flat. But of course for me personally an answer for the Opel is totally fine.
    – AndreKR
    Feb 15 at 23:05

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The direct question about leakage

The parasitic battery draw should be VERY low - just keep-alive for clock, radio stations and powertrain computer. A few milliamps. You should be able to park a car for 2 months (1500 hours) without flattening the battery. A typical battery is 75 amp-hours. So 50mA would be too much.

If you have draws higher than that, then something is broken, or some aftermarket things was installed and left on. Such as a USB "charger" always plugged into a DC power port, some gizmo plugged into the OBD2 port, a dashcam set to record while parked, or car comfort electronics that have a cellular modem trying to reach an obsolete (e.g. G3) network that no longer exists.

A guess about your alternator

some weird electrical issues where it randomly and suddenly drains the battery, sometimes while driving

Sometimes while driving!!??

No, that's a different problem. That is a faulty alternator. The alternator should be keeping the battery at 100%.

Here's the problem. You have no idea what your battery's state of charge is. You would not notice if the battery was 90%, 20% or 4% full. You notice when it is 0% full and stuff starts breaking! Once I got a low battery voltage light. The alternator had not just failed, it had failed several days prior and the battery finally got low enough to indicate.

So when you say "drains the battery", you really mean "has been draining the battery for quite some time". Or to be more precise, has not been topping up the battery like it's supposed to.

I suspect you do not have a power drain at all. When you come out and find the car at 0% battery, actually the car had been at 2% when you drove in the night before.

So I would focus on the alternator. With the alternator running, the voltage at the DC power port should be over 13.5 volts.

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  • OBD2 port indeed! I struggled with a Merc flattening the battery far too fast - 6 days - for nearly 2 years before I figured out NOT leaving the dongle in the port made all the difference.
    – Tetsujin
    Feb 18 at 12:48
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Paulster2's comment is spot-on: there is no single current drain number that applies to all cars. If you can find an Opel forum, someone there may have measured current drain on a 2014.

In general terms, about an amp for a few minutes after shutdown reducing to a couple hundred for an indefinite time is higher than normal. I would expect something more like 250 mA for a few minutes dropping to 50 or less to be closer to normal.

If you have an 80 AH battery with a 200 mA steady current drain, it will be discharged about 40% in one week. That's not normal. A car without excessive current drain should start without problems after sitting for a month.

If you have an aftermarket alarm system you might try removing the fuse or disconnecting it temporarily to see if current drain improves.

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