How quickly will a car battery run out?

[Scania]

One of my workmates left his car while he was abroad and it started fine after a full 3 months sitting idle. It is only a 1.0 though, so your mileage may vary.

When I was on Stobart's, work got quiet in the new year so a fair few tractors got parked up, lease payments suspended/reduced due to pay by mile system etc, most were back in service by late April / May having stood since just after the new year slump, never had a problem with any of the "off lease" as we termed them at our depot. - a mix of 12.8 - 13.6 engines.

All relatively new vehicles which ran pretty much 24/7 (day & night shift trucks) , on the other hand, when I used to sleep in the cab overnight, if I didn't fast idle the engine for 10 minutes prior to going to bed (having used a microwave for tea & then watched a film on an inverter powered laptop) it wouldn't start in the morning.....

 

[snapdragon69]

Many cars have buggy software and highly equipped ones can have issues with things waking up such as from faulty sensors in door handles etc... they also mitigate this by detecting the battery state and gradually stopping things like air suspension from periodically waking up and leveling the car but even then there may be software 'issues'. If you want a car stored at your bug-out hideaway a basic one is better and the battery will last many months.

 

[vanpeebles]

Many cars have buggy software and highly equipped ones can have issues with things waking up such as from faulty sensors in door handles etc... they also mitigate this by detecting the battery state and gradually stopping things like air suspension from periodically waking up and leveling the car but even then there may be software 'issues'. If you want a car stored at your bug-out hideaway a basic one is better and the battery will last many months.

Sounds like my Disco! They are like KITT! it wakes up now and then to assess what’s going on, hammers the battery.

 

[Paul_RD]

Depends on the electrical loads when all is off and the vehicle is off.
I've got an old Land Rover and it lasts several months.
I also got a ten year old Mazda and anything more than a couple of weeks (at the moment) and it won't start.

 

[Resident]

If a car (Mk. 5 VW Polo GTI) is parked in the street outside my house, with only the burglar alarm using the battery, how long will it take for the battery to lose power to the extent that it will no longer start the car?

Could you not buy a solar trickle charger and just leave the panel in the window (preferably one that will get most light)? On an average day the panel should replace what the alarm drains

 

[gEd]

I left my 2003 V70 parked up on the street from Feb to April (inc some pretty cold spells) for a full 2 months due to lock down, me working from home and having covid...
She started on the button which was a big relief as I was worried that she'd be flat after that amount of time.
Battery is pretty big and only replaced 18 months ago but and had been run flat once when garage kindly left my light on for me.

 

[DanTheMan]

Our 2nd car was idle for 2 months at the beginning of lock down and started fine. It is only a 1.25 fiesta with barely any electronics and had a new battery 2 years ago.

I can confirm that if you leave your key in the car and turned to the ignition on position whilst it sits on the driveway, it won't last a week. Hence the need for a new battery

 

[Bobmunkhouse]

3 weeks for new car with keyless entry I found...

 

[Howard]

I don't know what is considered normal parasitic battery drain but after some googling, it seems around 50-75mA is the norm, with some suggesting it should be as low as 25-30.

Google also seems to suggest that this generation of Polo GTI would probably be fitted with a 60-65Ah battery.

So let's say 60Ah and 60mA current draw.

It will take 1 hour to drain that battery with a 60A load, so with a 60mA load it will take, in theory, 1000 hours or 41 days to drain, or 50 days with a 50mA load, 100 days with 25mA, and so on.

Edit: Above is of course in theory and assuming that the battery isn't old and worn out.

 

[Terminal_Boy]

You’re assuming a linear discharge which isn’t the case for an older battery, especially at higher rates of discharge.

 

[Django x2]

Well, typically, the maths don't support the real world. 3 cars, all short journeys, if any (the worst type for battery life conditioning). One a heavy everything electric Discovery, a V8 S6 used once a week for 10 miles and a SEAT ibiza that starts first time every time when I move it to the driveway for a wash, once every 3 weeks. No charging, no conditioning, no disconnecting.

 

[Howard]

You’re assuming a linear discharge which isn’t the case for an older battery, especially at higher rates of discharge.

Sorry yes I should have said that this would be with a good-condition battery.

 

[Jamauk]

My Focus ST225 managed three weeks garaged without issue in February. Has keyless entry which I know is a constant drain on the battery, along with the standard nav head unit that is always on standby.

it does really depend on the car and the options though. Plus some manufacturers cut costs by providing the cheapest battery they can get to maximise on profits, along with how often and how long the car was driven before being parked up.

 

[phil-k]

Could you not buy a solar trickle charger and just leave the panel in the window (preferably one that will get most light)? On an average day the panel should replace what the alarm drains

I have been using one of these, excellent to stop my battery draining

 

[Paul_RD]

If you can easily get a mains lead to the vehicle (not ideal if it's parked on the road outside), I would recommend one of those CTEK chargers - I have the CTEK MXS 5.0.

 

[Cyber-Mav]

even a small solar panel can extend time a fair bit.

 

[Paul_RD]

even a small solar panel can extend time a fair bit.

+1
Especially if it's parked on the road outside and a mains cable could be a trip hazard.

 

[ultralaser]

A while back I had an old Renault diesel and that would like < 10 days without being charged (I know that because I had to get the AA out to charge it after a holiday), and my Civic lasts seemingly forever. It does seems massively variable. With the Lithium quick starters so cheap it might be worth just buying on of those then you have no issues (plus they normally double as a phone / laptop charger too!)

 

[EdGey]

Some interesting replies here.

I've jut got back from a 7 month stint in another country, my car started first time.

Granted the battery was fairly new before I left and it's only a Ford Fiesta, but 30 days?

 

[GreatAuk]

It really depends on the car, some will drain far faster than others. My old Subaru would drain so low it couldn't be started after 2 weeks due to its aftermarket alarm, but i've had others which are fine after 2+ months like my old Toyota Yaris.

I think new subarus probably have this problem too... My parents' relatively new subaru was flat after a few weeks of lockdown, and as they didn't need to use it just left it until recently. Now needs jump starting every time, even though they tried a battery conditioner, so imagine it got completely drained and damaged . Sounds like the garage will replace it on warranty though.

I left my Toyota yaris on the drive for about 2 months after lockdown started, and had no problems starting it.