How long to leave a Car Battery flat

....before it becomes unusable. It was flat last weekend after 5 weeks self isolation. I bought a compact booster and started it on thursday, ran it for about 20 minutes, but today (Saturday morning) it is flat again. It's a relatively new car 2019 Golf R.

Reply to
John
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Why was the battery flat in the first place. A battery should hold its charge for longer than five weeks.

If the car is new shouldn't it be under warranty?

Reply to
Pancho

After 2 weeks, the electronics* in my car take the battery down to about

20% (according to my battery charger).

  • alarm, radio and other electronic devices continute to operate with then ignition switched off.

Reply to
charles

I think that once a car battery has been totally flattened, it's never going to be the same again. Sorry.

Reply to
David

thursday,

The chances are it's a dead battery, one could try charging it up again and going for a good run rather than a 20 min idle on the drive and seeing if it recovers. I doubt it will to be honest.

The "sleeping" drain of a modern car will flatten a battery in 5 weeks without too much trouble. Sometimes even quicker if it keeps getting woken a bit by the remote key unlocking of other cars nearby...

One could try but mentioning/admiting a 5 week period of no use wouldn't go in your favour. Read the user manaul for any precautions needing to be taken for a "long period" of non-use. How long is considered a "long period"? What you should have done? Read the warranty as well, that might differ from the user manual.

Reply to
Dave Liquorice

A care that new ought to have decent battery management. Even my old 2009 Transit based motorhome does stuff like deactivating the remote central locking when it?s left for a while.

My wife?s 2017 Yeti was absolutely fine when we went off to NZ for 5 and a half weeks.

Tim

Reply to
Tim+

The battery might but some modern cars have an insanely high standby current drain. Alarm, clock and USB ports often running 24/7.

They tend to need a decent run every 3-4 weeks or won't start. The older the battery gets the more TLC it will demand if you want reliability. The most annoying failure mode is when there is just enough left to start the car to make an outward journey but not enough to come back.

Immobilisers seem inclined to panic even if the battery has enough juice to turn the engine over but the voltage droop is excessive. That is how mine fails when left unused for too long. I have added a solar charger which at this time of year works reasonably well to extend the life.

Reply to
Martin Brown

It may be that it was 'flat' longer than you think.

Certainly, I'd expect (nearly) new battery to recover after a couple of days being left- our CRV used to be terrible if left for several weeks but it always recovered, even with a much older battery- after a charge with a charger.

Of course, it could be a duff battery- it does happen.

I'd try giving it a decent charge with a charger- not by running the car for just 20mins. A long drive may do it but, of course, that probably isn't an option.

Reply to
Brian Reay

I think you?ll find that the drain doesn?t continue at the same level though. A car that new ought to ?throttle back? the parasitic drains after a few days.

If a 4 year old Yeti can do it, I?m sure a 1 year old Golf can.

Tim

Reply to
Tim+

Ok. I just tested my car and it appeared to be using about 2mA quiescent. Which wouldn't drain the 40 Ah battery in five weeks.

But I take the point other cars my have more electrical gizmos than my very basic car, Vauxhall Corsa approx 6 years old.

Reply to
Pancho

Somewhere in the manual it might say that you should disconnect the battery if the vehicle is likely to be unused for more than three weeks. Is does in my 59-plate Astra manual.

Reply to
Andrew

A bloke that reads the manual?

Just say a bloke down the pub once told you...

Reply to
ARW

My Skoda will not if the dash cam is left plugged in.

Reply to
ARW

make, model?

Reply to
charles

On Sat, 18 Apr 2020 09:00:04 -0000 (UTC), John snipped-for-privacy@home.org wrote: [snip]

I think I shall print this thread and take it with me when go for a test run this afternoon :-)

Reply to
Scott

That is very very low. Sure it's not 20 mA?

Reply to
Dave Plowman (News)

What make so that I can avoid it?

Reply to
Richard

I have the battery off the car now ready for charging, but when the battery is back on the car, I will check the residual current when the ignition is off.

Reply to
John

Just don?t expect the initial drain to be the same as the drain over longer periods. Your Golf will almost certainly have some battery management system.

Tim

Reply to
Tim+

Hows things in Horsham.

Reply to
GB

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