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Flat Car Battery from non-use of car

How long before a car battery goes flat when car not used?

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Romeo Whisky01/04/2020 09:30:53
724 forum posts
202 photos

Like many on this forum, I am over 70 and therefore under "house arrest" for the duration. One thing that's worrying me is that my car - an automatic - has been standing on the drive outside, with the alarm (and other electronics?) steadily draining the battery. I have no means of charging the battery "off-line".

So I have two questions for "me learned friends" ...

1. When a car is not driven for some time, how long before the battery goes flat, assuming battery is in good condition, and was charged on a 30 mile journey prior to lockdown?

2. Is it possible to use a 3S 3200 LiPo (or perhaps two in parallel) to jump-start the car if its battery does go flat? (And how would you set that up?)

ken anderson.01/04/2020 09:34:27
8637 forum posts
779 photos

hello Romeo, why not just go out for a 20 min run,once,twice a week...not meeting anyone ect….I wouldn't fancy trying the lipo sure I read somewhere that a car standing with a healthy battery, would be ok for a few weeks...I may be wrong.

ken dept.

PeterF01/04/2020 09:38:33
525 forum posts
724 photos

I have left my car for 5 weeks before without it being a problem.

I would not advocate using a LiPo, car starter battery currents are typically many hundreds of amps, car batteries tend to be rated for things like 600 amps when cranking a cold engine.

Nigel R01/04/2020 09:43:49
3756 forum posts
587 photos

What Ken suggests.

Alternatively, parts shops are open (as an essential trade), perhaps a helpful friend or neighbour could pick up a charger for you, or, maybe lend you one? Halfords do a basic charger for £30.

Answer to #1 - piece of string. Our relatively recent battery (~1 yr old) in the diesel passat was being a bit sluggish after several weeks, it had been used only for short journeys for the preceding two weeks, ie the last decent run was a month ago.

Steve J01/04/2020 09:59:41
1841 forum posts
53 photos

If you are not using a car for an extended period of time, I would suggest getting a maintenance charger and leaving it connected.

PS If you don't have a conventional lead-acid battery, check that the charger is suitable.

Edited By Steve J on 01/04/2020 10:02:05

Denis Watkins01/04/2020 10:01:31
4335 forum posts
104 photos

Please allow some leeway in these hard times for generalisation as all cars are different

But in General, with modern equipment, the drain can be 100mah per day, approx 1A in 10. Days

A poor battery is no help.

But a good serviceable small car battery has 45Ah, so you can stand a couple of months easily.

Your Poor battery condition will now show up !

30 minutes has been mentioned, and will get you charged.

A serviceable electrical system will bring up a low battery in a small car after a 30 minute drive above, 2000rpm

This could mean 40mph, so pick a dual carriageway route

SIMON CRAGG01/04/2020 10:25:23
563 forum posts
5 photos

We use a small £10 solar panel proped up inside the windscreen and connected to the battery. Keeps the battery topped up pefectly.

Andy4801/04/2020 10:34:05
1497 forum posts
8 photos

We left both our cars for 6 weeks earlier this year, no problem at all.

Peter Miller01/04/2020 10:51:25
10966 forum posts
1272 photos
10 articles

I have a solar panel that sits on the dashboard and is plugged into the cigar lighter (Which is always ON)

I have had it for some years and one winter a car that I was selling sat out in the bitter cold for about a month I went out and it started first press on the starter.

I got mine ffrom Amazon. IT was the smaller of the two sizes listed at the time.


Peter Miller01/04/2020 11:08:10
10966 forum posts
1272 photos
10 articles

Funny, I came back and the post was still there even though it had gone up on the thread

Edited By Peter Miller on 01/04/2020 11:09:17

Cuban801/04/2020 11:20:50
2912 forum posts
1 photos

I have a maintenance charger connected up to my motorbike over the winter months. Like a modern car, new bikes are constantly drawing from the battery when not in use to feed alarm systems, immobilisers and other electronics. My Oxford maintenance charger monitors the battery voltage and when it drops below 12.6V, it applies a couple of hundred milliamps until the voltage rises to about 13.8V and then drops the current back to zero - the cycle repeats every couple of hours or so. What it's doing is displayed on an LCD screen.  A standard battery charger for long term use is not advisable as it will usually drop to a low current and maintain a small charge indefinitely - this may lead to overcharge and possible damage to the battery over a long period e.g. over winter for several months. Car chargers will differ and some might have a maintenance mode, but I have known a few cheaper types that will constantly stuff an amp or more into a fully charged battery come what may.

The solar panel into a cigar lighter socket is a good idea, but some cars might disconnect the socket from the system after a time delay. My 08 Mondeo keeps the sockets connected, but the wife's 15 Fiesta doesn't.

Edited By Cuban8 on 01/04/2020 11:24:28

Engine Doctor01/04/2020 11:27:59
2469 forum posts
39 photos

Hi Romeo Whiskey . Most modern cars have sophisticated electronics that draw tiny current even when at rest. Provided your battery is in good condition it should be ok for at least three weeks and probably longer . If you can run a lead out to you car then a Ctek or similar charger/conditioner will maintain your battery for long periods of for the Absaar model that is somewhat cheaper but a good little charger. I bought one of these a few years back and use it during the winter months when car is standing. If you do go for one of these make sure you buy one of sufficient capacity for you battery .

I did buy a solar powered battery trickle charger some years ago and was  not impressed but solar panels have improved so may be a better option no summer is on its way ?

Another thing to think of during long lay ups is the general condition of the car , brakes etc . They will benefit from a drive around the block once in a while enough to get them hot and dry out any moisture that can cause corrosion .

lets hope it all goes well.

Keep safe keep well and keep your distance smiley


Edited By Engine Doctor on 01/04/2020 11:34:59

John Wagg01/04/2020 11:43:32
66 forum posts
10 photos

Just a thought - the chargers that plug into the cigarette socket may not be connected to the battery ?

The ones in our car do not work unless the engine is running. Not sure if that means there is no connection to the battery if the ignition isn't on?

I charge my motorbike through the socket with no problems.

Paul Marsh01/04/2020 12:35:15
3970 forum posts
1190 photos

You can still drive the car. I've got 2 cars, and take one out once a week to keep the battery charged, but found that both vehicles. As I didn't use one for over 4 weeks, as used the other for work (the V6 Vectra is mainly for shows) and when i did start it, started fine. But both batteries are new and in good condition. It takes around 20 mins of running to recharge an extended start, so if the car starts easily a drive for 20 to 30 mins at high speed should keep enough charge to enable future restarts.

Martin Harris01/04/2020 12:47:23
9264 forum posts
245 photos

Assuming that like most people on this forum, you have a multiple battery technology charger for model use that runs on 12v, you could charge your car battery on a Lead-Acid program using those LiPos as the power source. Much kinder on the cells, terminations and cabling than using them to jump start although I have heard of people using them in this way for emergencies.

kc01/04/2020 13:25:15
6427 forum posts
173 photos

Buy a pair of jump leads now before everyone realises they have the same problem in a couple of weeks.....

Then if you are a glow/petrol flyer then use your 12 volt model starter battery to start the car. Or if an electric flyer keep your car battery charged with your lipo charger set to lead acid. But if you are just a glider pilot bad luck - on your bike!

Seriously our little 12 volt batteries will start a car. Years ago at a show the seller of those cheap ex standby equip 12 volt 7 ah gel cells   ( Proops i think ) said he used one of these cheap batteries to start his E type - I didn't really believe it but later found he was correct. They will start a car.   However take all the precautions we used to take when running old cars in the 1960's in the 62/63 freeze. Free up the engine first by rocking the car in gear ignition off as the oil will be sticking a bit ( obviously we used a starting handle then! Younger people ask your grandfather what they are) Then keep your foot off the 'gas' and turn it over twice. Leave a minute try again. Repeat until it starts ensuring you dont touch the accelorator, if you have then keep the throttle wide open and turn the engine over with throttle wide open then leave a few minutes.Try again. If all else fails then its a push start - try using 3rd gear not 1st and get the car really moving before dropping the clutch. My car eventually started every day in the 62/63 freeze even though it was an old 1950 A40 Devon with ancient battery.

Edited By kc on 01/04/2020 13:48:15

Cuban801/04/2020 13:45:52
2912 forum posts
1 photos

A whiff of the wonderfully named 'Start Ya B*****D' or good old Easy Start does help. The old timers even used to use model Diesel fuel for the Ether content I believe.

SR 7101/04/2020 14:40:57
433 forum posts
140 photos

I have started my car a couple of times with a 3s 3000 lipo, swung it over fine

Romeo Whisky01/04/2020 14:45:28
724 forum posts
202 photos

Thanks guys, info much appreciated. I always keep jump leads in the car as it's an auto, but cannot get another car very close to where I have to park it at home.

Also I can't easily use a trickle charger as there is no power point handy and the driveway is open plan. The idea of using one of my lipo chargers set to Lead Acid and powered by a Lipo is certainly an option I hadn't thought of.

I realised that taking it for a drive once a week is the obvious answer, and have done that with my wife's car, but as we depend on various neighbours to bring us food essentials I don't want them to get the wrong impression that we are flouting the govt rules. I also don't know how the local stasi would respond if I explained that's what I'm doing.

While we're on that subject I don't understand why plod is harrassing people exercising or walking dogs when they are clearly well above two metres away from anyone else. Don't they realise that for many people the beach or countryside is their local area?

Chris Walby01/04/2020 14:51:21
1200 forum posts
299 photos

I would be inclined to take the car out for some exercise once a week for 30 minutes at a moderate speed


If it fails to start when exercising it you can fix it

If you need it in an emergency you know it will start

If you get stopped by Plod just say you are over 70 and the car may be needed in an emergency + you are going out for essential supplies - petrol

All other options involve tinkering which is okay if you have the time, skill and equipment to do so.

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