Battery Maintenance

maninthestreet

I've been driving cars for over 30 years and have never once had to replace a battery - am I just lucky??

Richard53

maninthestreet wrote: »

I've been driving cars for over 30 years and have never once had to replace a battery - am I just lucky??

Yes, unless you change your cars frequently. It depends on the car, but I generally find that batteries last me about 6-7 years. I live in a fairly isolated spot with virtually no public transport, so I tend to replace them before they fail. If it's starting to spin the engine slowly and I've had 6 years out of it, I have no hesitation in buying a new one. At under a tenner a year, it's worth it for peace of mind.

If someone buys only new cars and trades them in at 3 years, he or she would probably never have to buy a new battery.

Ectophile

missile wrote: »

Batteries do not suddenly fail "out of the blue".

Oh yes they do. Not very often, but I've had it happen to me once.

I was leaving work one day. Started the car no problem, but stalled it maneuvering around the car park. Went to start it again, and the battery just died. As soon as I turned the key to Start, all the lights went out.

Luckily, there was just enough power to run the ignition system, so someone could push start me. After a 52 mile drive home, the battery was still dead.

Terry98

Ectophile wrote: »

Oh yes they do. Not very often, but I've had it happen to me once.
.

Yes it happened to me as well that is why I posted the question.

If I had any idea the battery was going to go I would have done something about it.

One morning, out of the blue, the car would not start and for the first time in over twenty years I had to call out the AA. It took them two minutes to say the battery was dead and I needed a new one. Apart from the inconvenience the whole thing cost nearly £200.

I don't want that to happen again!

reeac

Let's say 360 amps for 10 seconds use of starter motor. That's 1 Ah taken from the battery. Shouldn't take long to replace that.

Strider590

reeac wrote: »

Let's say 360 amps for 10 seconds use of starter motor. That's 1 Ah taken from the battery. Shouldn't take long to replace that.

Using your figures and assuming a standard 4A charge, 1Ah would need 15mins and I guess that's a close enough approximation, it could take twice as long in the winter due to temperature.

However the reality is not so simple, the more full a battery is the slower it's charge rate, a battery is quite slow to absorb a charge and once the battery terminal voltage reaches 13.4v your voltage difference is just 1 volt, so that last bit of charge takes quite a lot longer. In fact most cars never fully 100% charge their own battery, and herein lies the problem, a lead acid battery slowly ages and deteriorates at anything less than 100% charge.

People think of batteries in very linear way, but they don't behave this way at all.



Would suggest that resistance almost doubles at under 0°C, which means charge current halves and charge time doubles, but again this probably varies.

AdrianC

Strider590 wrote: »

Using your figures and assuming a standard 4A charge, 1Ah would need 15mins and I guess that's a close enough approximation, it could take twice as long in the winter due to temperature.

4A charge?

On a normal domestic battery charger, yes. On an alternator...? Nope. Most modern stuff has 90-100+A alternators.

Strider590

AdrianC wrote: »

4A charge?

On a normal domestic battery charger, yes. On an alternator...? Nope.
Most modern stuff has 90-100+A alternators.

Yes, but they don't charge the battery at that rate, that's 90A short circuit @ 14.4v.
Your battery is probably never much below 12.8v, so your charge current is the voltage difference of 1.6v divided by the internal resistance of the battery.

The only way increase that current is to increase the alternator voltage, which I believe is what Fords smart alternators do.

Ectophile

reeac wrote: »

Let's say 360 amps for 10 seconds use of starter motor. That's 1 Ah taken from the battery. Shouldn't take long to replace that.

If a modern car takes 10 seconds to start, there's something wrong with it.

I'd say more like 2 or 3 seconds for a petrol. A diesel may require a few seconds of preheat first, but should still start in under 5 seconds.

Which is why you can get away with pootling around town doing lots of short trips, and never have to get out the battery charger - despite what the doomsayers may say.

reeac

Ectophile wrote: »

If a modern car takes 10 seconds to start, there's something wrong with it.

I'd say more like 2 or 3 seconds for a petrol. A diesel may require a few seconds of preheat first, but should still start in under 5 seconds.

Which is why you can get away with pootling around town doing lots of short trips, and never have to get out the battery charger - despite what the doomsayers may say.

I was deliberately using big numbers to be on the safe side. I think that I'd agree with 2-3 seconds although I've never timed it. Realistically in many cases the charge taken must be nearer 0.2Ah..
As I think that I've said before here, I've never charged my two everyday cars from an external source over battery lives of 10 and nearly 14 (and counting) years and neither does a big annual mileage.