Idle running a car to keep battery topped up whilst SORN

36
Posted 26th May
Hi folks,

apologies if this has been asked before.

I SORN'd my car at the beginning of the month and it hasn't been turned on or driven since.
Just started up absolutely fine (almost 4 weeks now) and I want to leave it running to get the battery topped up.

The battery was only replaced around 3 months ago and it's an VARTA EFB 85Ah.
My car is a 2.2D Mazda 6

Would 30 minutes be ok or should I let it run a little longer?

I don't have a battery charger and don't fancy buying one as I am trying to keep my purchases down due to unknown job security with the wife etc...

any help is greatly appreciated
Community Updates
Ask
36 Comments
You could alway's just disconnect the negative terminal on the Battery, problem solved
regretful126/05/2020 10:57

You could alway's just disconnect the negative terminal on the Battery, …You could alway's just disconnect the negative terminal on the Battery, problem solved


Disconnect the battery would be your best bet as regretful1 said
A cheap trickle charger. This sort of thing NOT suggesting this one in particular I don't know it.
A disconnected battery will still go flat just more slowly.

ebay.co.uk/itm…DEI

We have an auto shut-off one the comes on everyday on a time switch for a few hours but turns itself off if the battery is fully charged.
Edited by: "joyf4536" 26th May
Running a car on "idle" won't do much at all. You need to run the engine and keep the revs between 1500-2000rpm for about 10 mins to make the alternator work efficiently. Just letting it idle can mean more "power" has been used than is going in. Starting an engine pulls a lot more power from a battery than most realise.

Battery chargers really don't need to be expensive. An "intelligent" charger off Ebay or a Lidl (£15) jobbie will be sufficient to keep the battery in great condition. Maintenance charge about once a month is fine.
hadn't thought of disconnecting the battery, but makes sense.
will have to reprogram the radio, seats and what not afterwards I guess
Nad_8426/05/2020 11:11

hadn't thought of disconnecting the battery, but makes sense.will have to …hadn't thought of disconnecting the battery, but makes sense.will have to reprogram the radio, seats and what not afterwards I guess



Don't forget - disconnecting the battery is fine but do you still have current insurance on the car? If you do (or not) and the car has an alarm system - it WILL be non-functional. Perhaps security isn't an issue for you?
Phsycronix26/05/2020 11:14

Don't forget - disconnecting the battery is fine but do you still have …Don't forget - disconnecting the battery is fine but do you still have current insurance on the car? If you do (or not) and the car has an alarm system - it WILL be non-functional. Perhaps security isn't an issue for you?



That's a good point! I do have insurance and it definitely states it has a working immobiliser and alarm.
OK then back to the original question, how long does it need to run for?
I've wedged the accelerator down so it's sitting at 1250 RPM, heaters on full blast and it's been running for about 25 minutes.
I'll give it another 10 then switch it off
If you are going to run the engine to charge the battery dip the accelerator after starting, on older cars at least the alternator needs to reach so many revs before cutting in (at's OK after it has cut in). Probably different on modern cars.
Hopefully you've not left your car unattended while running it, because that would probably invalidate your insurance too. Seriously, a £15 supermarket battery charger with auto shutoff would be a worthwhile investment if your car remains idle for another month, that way you can be sure your battery is fully charged each time. Also, remember to disconnect the battery from your car while charging, some alternators don't like the charging process.
joyf453626/05/2020 11:24

If you are going to run the engine to charge the battery dip the …If you are going to run the engine to charge the battery dip the accelerator after starting, on older cars at least the alternator needs to reach so many revs before cutting in (at's OK after it has cut in). Probably different on modern cars.



thanks, it's a 63 plate and has stop start so assume that is classed as modern. but I am sure a bit of revs will help
wibbleboy26/05/2020 11:28

Hopefully you've not left your car unattended while running it, because …Hopefully you've not left your car unattended while running it, because that would probably invalidate your insurance too. Seriously, a £15 supermarket battery charger with auto shutoff would be a worthwhile investment if your car remains idle for another month, that way you can be sure your battery is fully charged each time. Also, remember to disconnect the battery from your car while charging, some alternators don't like the charging process.


Don't worry it's around the back of the house, I can see and hear it running and the doors are locked and I have the keys as it is a keyless car
Nad_8426/05/2020 11:17

That's a good point! I do have insurance and it definitely states it has …That's a good point! I do have insurance and it definitely states it has a working immobiliser and alarm.OK then back to the original question, how long does it need to run for?



Well, as previously said - idling is no good. I could quote chapter and verse but if you "Google" the subject there are many folks who know this fact. Take as an example, a large saloon car will take upwards of 100Ah "draw" to start the engine. If you then "idle" the car, thinking you are 'charging' the battery, after about 15 mins it will only put about 4-5 amps back in! Therefore, each time you did this it would effectively lower the batteries capacity more and more - rather than keep it healthy. Er-go, battery dies...

The issue is, most people do not wish to sit in their car for 15-20 mins revving the engine to over 1000rpm (over 1500 is better) - looking like a 'nana' to anyone watching. LOL! I really can with a good conscience only recommend that you get a little charger. Just make sure it has the "amps" range to handle your size battery. Again, some of the cheap "China" sold chargers are for small batteries only.
Aren't you supposed to turn over an engine every few months to oil the cylinders and circulate the coolant etc, and roll it so that the tyres don't permanently sit on the same spot damaging them, if you haven't jacked it up.

I believe you are also supposed to put a fuel stabiliser in the tank to stop the fuel deteriorating and causing blockages, and fill the tank full to prevent rust.
Edited by: "melted" 26th May
I understand you don't want to spend too much at this time, however what you're doing might be false economy. You'll have wasted 15 quids worth of fuel by the time this over.

Getting a charger will be much better than a ruined battery and / or wasted diesel.

You must check the chargers will be compatible with your battery.

40876260-UzAQi.jpg
Just over a tenner can get you a charger, alternatively use a multimeter to check the voltage of the battery before you turn it over. The might be days where the voltage hasn't dropped and you're unnecessary charging it.

Edit:
You have a big diesel so the below would be better.
40876260-0AlsT.jpg
Edited by: "mogsog" 26th May
mogsog26/05/2020 12:35

I understand you don't want to spend too much at this time, however what …I understand you don't want to spend too much at this time, however what you're doing might be false economy. You'll have wasted 15 quids worth of fuel by the time this over. Getting a charger will be much better than a ruined battery and / or wasted diesel. You must check the chargers will be compatible with your battery. [Image] Just over a tenner can get you a charger, alternatively use a multimeter to check the voltage of the battery before you turn it over. The might be days where the voltage hasn't dropped and you're unnecessary charging it.Edit:You have a big diesel so the below would be better. [Image]


Thank you, what website are you looking at here btw?
Nad_8426/05/2020 12:52

Thank you, what website are you looking at here btw?


Sorry, it's the Aliexpress app so unfortunately the would be a shipping delay as it comes from China. Sadly nothing in the UK comes close in price.

I mean, I don't want you buying one, then lockdown is over and it doesn't come until after so exercise your own judgement.

If you know you're going to be off for significantly longer due to circumstances in your industry then it may still be worth waiting for a China charger.
Edited by: "mogsog" 26th May
I just un-SORN'd the car after it was off road all of April and until the slight easing of the rules earlier this month. Slightly annoying forking out £23 for half a month's tax, but seemed less hassle to just use it occasionally than to keep starting it up once a fortnight, running the aircon, rolling it back/forth etc.
At 3AM, take your car for a spin back and forth on your road and come back.
Edited by: "zworld" 26th May
zworld26/05/2020 13:02

At 3AM, take your car for a spin back and forth on your road and come …At 3AM, take your car for a spin back and forth on your road and come back.


I've got kids and cherish my sleep
Stop start batteries aren't cheap so do what it takes to keep the battery healthy !
If you have space, drive forward and backwards a bit to help prevent the brakes from rusting on.
Nad_8426/05/2020 13:06

I've got kids and cherish my sleep



Once a week, I am sure you can change the norm.
If you would like a very cheap trickle charger then ebay has this one which the seller appears to be in the UK - Car Battery Charger Starter Master NEW 12V 0.5 Amp Trickle Autocharge ebay.us/26sWZs under £8

This charges at 0.5 APH so if your battery was flat it would 190 hours! If you wanted something better then go for 4-8 amp battery charger which would be quicker and more useful for battery charging if for instance the battery drains by accident like the Maypole mentioned by MrWalle for around £20
I'd go for a portable car jump starter charger. Dearer than a trickle charger, but then you don't need to leave it attached to the car the whole time. Obviously best to make sure it is fully charged by plugging in to an ordinary plug sock indoors or in a garage. My son got one as a Christmas present and over the last few weeks it has been the best present ever!
Nad_8426/05/2020 11:22

I've wedged the accelerator down so it's sitting at 1250 RPM, heaters on …I've wedged the accelerator down so it's sitting at 1250 RPM, heaters on full blast and it's been running for about 25 minutes.I'll give it another 10 then switch it off


Why have the heater and fans on draining the battery you are trying to charge?
Uridium26/05/2020 16:25

Why have the heater and fans on draining the battery you are trying to …Why have the heater and fans on draining the battery you are trying to charge?


Hot day, so if the car were to overheat whilst sat with the engine running it lets some of the heat escape
Funnily enough there is currently a Youtube advert from the AA that says that you should start the engine and let the car idle for 15 minutes to keep the battery in good condition, which seems to contradict everything that I've ever heard about battery charge, but they are supposedly the experts so...
Nad_8426/05/2020 16:29

Hot day, so if the car were to overheat whilst sat with the engine running …Hot day, so if the car were to overheat whilst sat with the engine running it lets some of the heat escape


The running of the car fans etc is not required, the car will keep the heat in the engine until it is up to temperature then the thermostat will open and the water will begin to flow round the radiator. Only once the radiator stops cooling will the engine Fan cut in to draw cool air across the radiator to reduce the water temperature.
How long are you planning on keeping your car SORN?
I use this on one of my cars and it's been perfect..

TheAA 12v car solar charger..

amazon.co.uk/dp/B07PBNV8L4/ref=cm_sw_r_apa_i_JUuZEb7XF3J22

Edit: just to add that on some cars if you use the aux port it may not work as they are sometimes disconnected from the battery when the ignition is off, so either direct connect it or use the eobd port.
Edited by: "bluetba" 26th May
bluetba26/05/2020 18:04

I use this on one of my cars and it's been perfect..TheAA 12v car solar …I use this on one of my cars and it's been perfect..TheAA 12v car solar charger.. amazon.co.uk/dp/B07PBNV8L4/ref=cm_sw_r_apa_i_JUuZEb7XF3J22Edit: just to add that on some cars if you use the aux port it may not work as they are sometimes disconnected from the battery when the ignition is off, so either direct connect it or use the eobd port.


What does this do and how is connected to the battery?
bluetba26/05/2020 18:04

I use this on one of my cars and it's been perfect..TheAA 12v car solar …I use this on one of my cars and it's been perfect..TheAA 12v car solar charger.. amazon.co.uk/dp/B07PBNV8L4/ref=cm_sw_r_apa_i_JUuZEb7XF3J22Edit: just to add that on some cars if you use the aux port it may not work as they are sometimes disconnected from the battery when the ignition is off, so either direct connect it or use the eobd port.


Had one similar, worked fine until I parked the car in the garage!
rimalpatel00726/05/2020 21:56

What does this do and how is connected to the battery?


It trickle charges the battery using solar power, i chose this one because it has protection so it won't over charge the battery.

You connect it directly to the battery using the clips or the oedb port on the car if you have one which is more convenient, stock the panel inside on the dashboard and it will trickle charge the battery.
joyf453626/05/2020 21:59

Had one similar, worked fine until I parked the car in the garage!


That can be an issue, unless your garage is made of glass :/
Post a comment
Avatar
@
    Text