Battery issues

Burgerphone

Hi all,

So a few months ago, I left my sidelights on in my car for about 2 days. I know that sounds stupid... but I'd put them on because it was slightly overcast so, when I got out of the car, I'd forgotten they were on and I couldn't see them shining on the road to remind me. So as you can imagine, the battery was pretty dead; the central locking wouldn't even work. No power whatsoever. So I jump started it and I ran it about for 20 minutes or so. By the next day, it had died again, so I charged the battery for a few hours through a mains charger.

It seemed fine for a while, I was driving it pretty regularly, every couple of days or so, around 5 miles to work and 5 miles back. The battery didn't cause me any problems for a while.

More recently, I've changed jobs and started sharing a lift with a few people, so I'm not driving it very regularly. One week, I drove the car for 5 days straight, about 18 miles a day, then after that, only drove maybe one short journey within two weeks. I live in a small town, so apart from work, I don't use my car much. The battery was then pretty flat again, although the radio/central locking still worked. This was mid December.

Earlier this week, after leaving the car for 5 days, it wouldn't start. The last time I'd driven it was a 14 mile round trip to work. Again, central locking worked, radio, lights etc. I thought 5 days seemed a pretty short time for the battery to lose power, so I've been disconnecting it whenever I've left it stood for a time (I did this in December when I left it for two weeks over Christmas and it helped keep the battery charged).

I took the car to halfords today for a battery check. They said the alternator and starter motor were fine, but that the battery needed replacing. So now I've got a new battery, but I'm worried about my routine affecting its life. Could the battery's performance have been affected by the first time it went flat, since it had no charge left in it at all? How long is too long to leave it without driving? Should I carry on disconnecting the battery when leaving overnight/for a few days/for a week? Or should it be fine now that I've got a new battery?

Sorry for all the questions - it's just the worst thing when you're about to set off to work and the car won't start...

Joe_Horner

You shouldn't have a problem. In fact, your old battery probably had some life left in it but a new one won't hurt.

From completely flat (as it would be with 2 days of lights on) you'd be looking at a good 24 hours of mains charging to get it back to a full charge. A "few hours" will have given it enough to get you going but still left it well down.

Consider that most car batteries have a nominal capacity of at least 35Ahrs and most domestic chargers give an average charge rate of around 2 - 3 amps (as opposed to the maximum rate they quote on the label). Charge rate will be low to start with, peak around mid charge, then tail off again as the battery voltage rises towards full. That means that, if everything was 100% efficient, it would take at least 12 to 17 hours to fully charge a completely dead battery. With losses, that means at least 24 hour charge to get it full from really empty.

From there, your use pattern won't have had a chance to regain the (maybe) 70% of charge that it was still missing, especially at this time of year when you're likely to be using lights, wipers, demisters and so on.

Most car batteries on "short use" cars will overall lose a little charge through the winter - or at least barely "keep up" - but it doesn't matter if they're well charged to start with because, when spring comes and the lights and wipers go off, they get to recuperate ready for the next year.

If, on the other hand, they're starting from a borderline charge (as yours was), they never make it through to spring!

Burgerphone

Joe_Horner wrote: »

You shouldn't have a problem. In fact, your old battery probably had some life left in it but a new one won't hurt.

From completely flat (as it would be with 2 days of lights on) you'd be looking at a good 24 hours of mains charging to get it back to a full charge. A "few hours" will have given it enough to get you going but still left it well down.

Consider that most car batteries have a nominal capacity of at least 35Ahrs and most domestic chargers give an average charge rate of around 2 - 3 amps (as opposed to the maximum rate they quote on the label). Charge rate will be low to start with, peak around mid charge, then tail off again as the battery voltage rises towards full. That means that, if everything was 100% efficient, it would take at least 12 to 17 hours to fully charge a completely dead battery. With losses, that means at least 24 hour charge to get it full from really empty.

From there, your use pattern won't have had a chance to regain the (maybe) 70% of charge that it was still missing, especially at this time of year when you're likely to be using lights, wipers, demisters and so on.

Most car batteries on "short use" cars will overall lose a little charge through the winter - or at least barely "keep up" - but it doesn't matter if they're well charged to start with because, when spring comes and the lights and wipers go off, they get to recuperate ready for the next year.

If, on the other hand, they're starting from a borderline charge (as yours was), they never make it through to spring!

Ah yes, forgot about the effects of cold weather too! I suppose that's why it was fine from april (when it first went flat) until december. Thanks for your reply.

facade

You aren't driving it enough to keep the battery charged.
Not being fully charged will kill a starter battery before too long.
The best thing would be a battery tender (a type of charger that you leave connected forever) but it reads as though you are parking on the road, so a mains connection is out of the question.

Those solar chargers are rubbish BTW, if they are working through the windscreen, and get stolen if you leave them on the roof.


Removing the battery, and charging it in the house is possible, as is disconnecting it if you leave the car for a week, but both these methods are a real pain if you need to use the car and it is raining, also modern cars don't really like having the battery continually disconnected and reconnected.

The only viable idea is to make sure the car gets run for at least an hour a week at driving speeds, not just left ticking over.

C_Mababejive

I had the same problem recently. My car is just about five years old and on original battery. I only use it maybe once or twice a week and as the winter came on , i found it would be sluggish to start or dead. I checked the alternator output..all good,,battery standing voltage was also good. After some reading i realised batteries, like a lof of things,rent what they used to be.

Went to the fabulous

http://www.eurocarparts.com/

Bought new battery for very reasonable price..fitted,,no problems since. Can leave car for weeks and it still starts easily.

reeac

C_Mababejive wrote: »

After some reading i realised batteries, like a lof of things,rent what they used to be.

.

Not sure about that. I have one car with its 9 year old original battery, another with its 12 year old battery and a classic car which has needed new batteries (2x 6 volt) every 10 years for the 32 years that I've owned it. Any of them will last weeks of idleness without flattening its battery.

facade

"Modern" cars tend to drain the battery after a few weeks sitting idle, they have new fangled things like alarms, and computers that continually draw a small, but significant, current.

benham3160

Modern battery types won't ever fully recover from "flat", the firm I used to work for suggested a modern zero-maintenance lead-acid would be permanently damaged at 10.5ish V.

It's just time for a new battery, to be really honest.

petrolhead69

Yep, draining totally flat damages the plates on a normal car battery, thats why caranans and motorhomes need more expensive deep cycle batteries. You should be ok with the new one. If the car sits regularly for a long time stick a solar trickle charger on the parcel shelf.

Strider590

Burgerphone wrote: »

Hi all,

So a few months ago, I left my sidelights on in my car for about 2 days. I know that sounds stupid... but I'd put them on because it was slightly overcast so, when I got out of the car, I'd forgotten they were on and I couldn't see them shining on the road to remind me. So as you can imagine, the battery was pretty dead; the central locking wouldn't even work. No power whatsoever. So I jump started it and I ran it about for 20 minutes or so. By the next day, it had died again, so I charged the battery for a few hours through a mains charger.

It seemed fine for a while, I was driving it pretty regularly, every couple of days or so, around 5 miles to work and 5 miles back. The battery didn't cause me any problems for a while.

More recently, I've changed jobs and started sharing a lift with a few people, so I'm not driving it very regularly. One week, I drove the car for 5 days straight, about 18 miles a day, then after that, only drove maybe one short journey within two weeks. I live in a small town, so apart from work, I don't use my car much. The battery was then pretty flat again, although the radio/central locking still worked. This was mid December.

Earlier this week, after leaving the car for 5 days, it wouldn't start. The last time I'd driven it was a 14 mile round trip to work. Again, central locking worked, radio, lights etc. I thought 5 days seemed a pretty short time for the battery to lose power, so I've been disconnecting it whenever I've left it stood for a time (I did this in December when I left it for two weeks over Christmas and it helped keep the battery charged).

I took the car to halfords today for a battery check. They said the alternator and starter motor were fine, but that the battery needed replacing. So now I've got a new battery, but I'm worried about my routine affecting its life. Could the battery's performance have been affected by the first time it went flat, since it had no charge left in it at all? How long is too long to leave it without driving? Should I carry on disconnecting the battery when leaving overnight/for a few days/for a week? Or should it be fine now that I've got a new battery?

Sorry for all the questions - it's just the worst thing when you're about to set off to work and the car won't start...

Yes, this is the one thing that will wreck a car battery faster than anything else.

With a new battery, leaving it for a week is no problem as long as you don't just use it to go 2 mile to the shop and back.

You could disconnect it and connect up a maintenance charger when not in use, but that's up to you.

pendragon_arther

I don't own a car but use a car club. All the cars automatically turn off the lights when left on by mistake after the ignition is turned off.