How long should a car battery work for if you accidentally leave lights on?

worded

Was in the car with the lights on wile parked

30 mins later the car won’t start

I left the centre cabin light on in the car another night and next morn the battery was dead

New battery time ?

Thanks

grogi

worded wrote: »

Was in the car with the lights on wile parked

30 mins later the car won’t start

I left the centre cabin light on in the car another night and next morn the battery was dead

New battery time ?

Thanks

Front lights require 2x55 W = ~110 W of power. Let's say 120 W with all the additional light sources. They are rated for 12 V, so they require 10 A of current. Over an hour the discharge is 10 Ah, so over half an hour the discharge would be 5 Ah.

The nominal capacity of the battery will not be smaller than 50 Ah. Leaving the lights on for half an hour should not discharge more than 10% of the capacity. It would not render the healthy battery incapable of starting the car. The battery is on its last legs now, especially when it was recently discharged as well.

Check the charging voltage of your car, it should be between 14.0 V and 14.4 V for optimal charging of the battery.

worded

Thanks

Got a jump start and in addition to everything else the battery clamp was very loose and it wouldn’t jump

Wiggled the bolt clamp on my car a few times tying to make it tighter and last attempt worked !

Close one

I think I will get a new battery anyway BUT the AA said the battery tests fine when the jumped it last time but perhaps this wasn’t a conclusive test

So two birds with one stone now. New battery and make sure the clamp is properly secure on both terminals.

Kind of happy this happened in day light on a dry day than over xmas on a rainy night .....

Alanstrainor

The cold kills batteries. If it's been a few years then maybe it's worth getting a replacement. Now that I think of it, mine has had the same battery for 6 years now... maybe I should get a new one too! :eek:

Basq

Funny this popped up..

Woke up this morning and mine was dead too. Got a jump start off father, took it for a spin, parked up with engine running for a while and then drove into work.

Currently parked outside work with jump leads in passenger seat in a prime location if I do need jump.. but hoping I don't.

Think I'll bite the bullet and buy a new battery though as it's a ten year old car bought used but don't think battery has ever been changed.

One thing I have noticed - which I look back at now as a sign - is that central locking took 2-3 times to register and unlock the car on repeated occasions over the last few weeks.

Will nip up to Halfords over lunch, and get it checked, and probably changed.

biko

Get a new battery of you like but it may not be needed.

I once left my light on for 30 mins and car refused to start.
Got jumped and went for a long spin to recharge battery fully, and didn't have any issues for a year until I sold car on.

Every car is different so what happened to me might be different from you..

Basq

biko wrote: »

Get a new battery of you like but it may not be needed..

Halfords said battery looks healthy.. 390A batttery with a reading of 390A. Got it from a Ford dealer last year so they may have replaced battery.

Remote central locking was sticky again before I left so I can't help but think that's possibly related. Frustrating but will keep an eye on things over next few days.

CiniO

grogi wrote: »

Front lights require 2x55 W = ~110 W of power. Let's say 120 W with all the additional light sources. They are rated for 12 V, so they require 10 A of current. Over an hour the discharge is 10 Ah, so over half an hour the discharge would be 5 Ah.

The nominal capacity of the battery will not be smaller than 50 Ah. Leaving the lights on for half an hour should not discharge more than 10% of the capacity. It would not render the healthy battery incapable of starting the car. The battery is on its last legs now, especially when it was recently discharged as well.

Check the charging voltage of your car, it should be between 14.0 V and 14.4 V for optimal charging of the battery.

While obviously all your calculations are good as always, I can't agree with your assumption of 120 W.

Two front bulbs 55W x 2 = 110W.
Rear tail lights (usually at least 2 bulbs per side 5W) so 20W.
Front sidelight bulbs 2x 5W = 10W.
Number plate lights 2x 5W = 10W.
Dash lights with plenty of small bubls most likely give another 50W or more.

Together over 200W, so over over 16A current.

Half an hour will take over 8Ah from the battery and in case of small car and small battery, this might be significent amount f.e. 40Ah battery, which is oldish and only has around 25Ah left, when drained by over 8Ah might be weak enough not to start a car.

However OP saying that leaving centre cabin light for the night makes car unable to start, seems to indicate that indeed battery is nearly completely gone.

irisheddie85

Basq wrote: »

Remote central locking was sticky again before I left so I can't help but think that's possibly related. Frustrating but will keep an eye on things over next few days.

This could be the battery in the key rather than the car battery

Basq

irisheddie85 wrote: »

This could be the battery in the key rather than the car battery

Yeah, I've noticed more electrical oddities so can't help but think it's battery related: https://touch.boards.ie/thread/post/105400475

Speedwell

Folks, indulge me while I have a "mom moment"... I know most people are never too far from a service station, a major road, or at least a mobile phone here in Ireland, but when I was a young girl in Texas, I learned to carry a jump-starter in my student-grade beater for battery emergencies. Well worth the cost. These days they are almost small enough to carry in your pocket and can be used as a portable charger for your phone.

A representative sample: https://www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=jump+starter Note that it's hard to get Amazon to ship batteries to the ROI, but the resourceful will find a (legal) way.

honda boi

Speedwell wrote: »

Folks, indulge me while I have a "mom moment"... I know most people are never too far from a service station, a major road, or at least a mobile phone here in Ireland, but when I was a young girl in Texas, I learned to carry a jump-starter in my student-grade beater for battery emergencies. Well worth the cost. These days they are almost small enough to carry in your pocket and can be used as a portable charger for your phone.

A representative sample: https://www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=jump+starter Note that it's hard to get Amazon to ship batteries to the ROI, but the resourceful will find a (legal) way.

Have an Aldi one for years now. Its a jump starter and compressor. I've used the compressor plenty of times. But never needed my battery jump started thank god.
Tho plenty of other people have used it on there batteries

MetzgerMeister

The battery in my 335i was on the way out after 1 year of ownership. I was left stranded once when the weather was this cold, didn't leave any lights on or anything like that.

BMW copped on with the F30 though as kinetic energy is used to charge the battery and it shows up on the dash when it's charging. Quite handy!

ohnonotgmail

Speedwell wrote: »

Folks, indulge me while I have a "mom moment"... I know most people are never too far from a service station, a major road, or at least a mobile phone here in Ireland, but when I was a young girl in Texas, I learned to carry a jump-starter in my student-grade beater for battery emergencies. Well worth the cost. These days they are almost small enough to carry in your pocket and can be used as a portable charger for your phone.

A representative sample: https://www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=jump+starter Note that it's hard to get Amazon to ship batteries to the ROI, but the resourceful will find a (legal) way.

i bought a very similar one from amazon recently and there was no problem shipping it directly to ireland.

this one. https://www.amazon.co.uk/gp/product/B06XBGPGKS/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

coylemj

The last time I had a car which would leave the headlights full on if you removed the key and got out, it was a 1981 vintage. My next car (1985) would step down full headlights to parking lights once you took out the key. My current car screeches like a banshee if I leave lights (other than parking) on and try to get out.

Voodoomelon

I've a 120Ah AGM in my 740, you'd think with that capacity it would be able to power anything. Not so unfortunately, just sitting eating lunch for 20 minutes with the radio one will usually pop up a "recharge battery" warning; once the car is in ignition 1, every module in the car seems to draw current.

Every few weeks i'll stick it on a trickle charge to keep it topped up, but short journeys doesn't help either.

I would have thought that lights on for anything beyond half an hour on average sized batteries would certainly drain it or at least not provide enough amperage to start, it's not an indication the battery is on the way out IMO.

Autochange

Some new cars have battery control modules which will shut down systems if consumers are left on when the battery reaches a certain discharge state.

beauf

Can be a cracked clamp or something else.

exaisle

worded wrote: »

<snip> in addition to everything else the battery clamp was very loose <snip>

This is the problem. Tighten the clamp. No new battery required.