Dead battery?

[Jahee]

Basically, i haven't treated the battery as well as i could have on this car, i let it drain flat more than a few times in the past year that i've had it.. Now winter has come i'm having real trouble with it.

Since its started getting to below about 8C consistently, its having trouble starting the car up, and in the last week, if its gone flat after about a day of not driving the car.

I'm 98% sure its the battery, the car cranks over fine, the remote locking is sluggish, and the interior lights are dim, which would tell me the battery is going. If i go for a long drive the battery charges up fine and is alright for a week or so, then drains flat again, so i'm guessing its not the alternator not charging the battery right.

Just wanted to be 100% before i buy a new one.

So, opinions?

 

[woodie1]

Sounds to me that you just need to change your driving habits (run the engine long enough to recharge the battery each time you start it) or buy a trickle charger.

.............If i go for a long drive the battery charges up fine and is alright for a week or so, then drains flat again,...............

A new battery will eventually act just like this one does if it has no chance to fully charge at least once a week.

 

[Jahee]

Originally posted by: woodie1
Sounds to me that you just need to change your driving habits (run the engine long enough to recharge the battery each time you start it) or buy a trickle charger.

.............If i go for a long drive the battery charges up fine and is alright for a week or so, then drains flat again,...............

A new battery will eventually act just like this one does if it has no chance to fully charge at least once a week.

Just to add, its a 3 and a half year old battery.

I'll give another example, after a 80 mile drive on friday, i then drove about 100 miles in the 7 days, on the 7th day, next friday, the battery was flat. This to me isn't normal behaviour for a healthy battery.

Am i wrong?

 

[boomerang]

It could be the battery and then again it could be a short that is draining the battery. If it's possible, after a long drive when the battery is all charged up, disconnect a cable or cables. If, after sitting, the battery is still fully charged, you know you've got a short.

That's not really considered old for a battery. But it could have a dead cell. That could result in the problems you're having.

Here in the states, we have several auto parts chain stores that will test a battery for free. You must remove the battery and take it in the store though. Anything similar there?

There's no way to tell from here which it is.

 

[cardiac]

You can go to an Auto Zone or a Napa store and they can load test the battery while it is in the car. Run it over to one of those stores and have them check it. This will give you the definitive answer......

Bob

 

[boomerang]

Originally posted by: cardiac
You can go to an Auto Zone or a Napa store and they can load test the battery while it is in the car. Run it over to one of those stores and have them check it. This will give you the definitive answer......

Bob

He's in the UK.

 

[Jahee]

Yea theres a place round the corner that does it, just gotta get it started first! I had to bump it by myself the other week, but i've got the flu at the moment and don't really have the energy! I'll have to call a friend.

If it was a short though, wouldn't the problem just come on all of a sudden, i've noticed a definate slow decrease it its capacity over the last few months..

 

[boomerang]

Completely discharging a car battery repeatedly is not what it's designed for. It's hard on it. Like I said it's hard to tell what's wrong from here.

I really think you've got a bad cell. The test will tell the tale.

I've got a lot of co-workers sick too. Hoping to let it slide right on by me.

 

[Jahee]

Yea.. Thats what im thinking.. I'm taking the morning off tomorrow anyway so i'll take it up there then!

Thanks for your help.

 

[steppinthrax]

Originally posted by: woodie1
Sounds to me that you just need to change your driving habits (run the engine long enough to recharge the battery each time you start it) or buy a trickle charger.

.............If i go for a long drive the battery charges up fine and is alright for a week or so, then drains flat again,...............

A new battery will eventually act just like this one does if it has no chance to fully charge at least once a week.

It dosen't take that long to charge a car battery by the alternator. It only takes a couple of mins depending on the current charge. If anything a bad battery in your car will damage your alternator or shorten it's life since the alternator has to work harder keeping the battery charged. And since the battery is bad it drains quite quickly when the car is off so when you start the car up the battery has to recharge.

Alternators today just top off the battery Lead Acid batteries don't discharge like other batteries when left dormant.

 

[imported_Truenofan]

yes, it actually does take a good min for it to charge the battery. your generating only so much power and it doesn't increase depending on rpm's. i had a brand new battery die in my car. I got a jump start, i had to let it run for at least 30-45min to get enough charge to start the car again if i let it sit for more than 10-15min. perfectly operating alternator, but it was the middle of winter which would be -30 to -40, but after 15-20min the engine bay is warm(which in the winter, you should let you car run for at least a good few min before you drive anywhere anyway, let the oil warm up and get up to temp and lubricate everything). so of course it may take awhile, but I'd expect you to need to let it run for awhile to get a full charge. its a battery like any other.

edit: besides, a 3 year old battery, i think its near the end of its lifespan(i think). check to make sure though.

 

[LTC8K6]

your generating only so much power and it doesn't increase depending on rpm's

I'm going to disagree.

The alternator's current output is low at idle and it does increase with RPM.

 

[desy]

Agreed
the higher the RPM the more current it can provide, think boost v trickle charge

 

[Thump553]

Three and a half year old battery is pretty old these days, cars put a whole lot more demand on the electrical system than they used to.

It's the beginning of cold weather season, I'd either break down and buy a new battery now or be prepared to walk/shiver/be late.

 

[steppinthrax]

Originally posted by: Thump553
Three and a half year old battery is pretty old these days, cars put a whole lot more demand on the electrical system than they used to.

It's the beginning of cold weather season, I'd either break down and buy a new battery now or be prepared to walk/shiver/be late.

I've had batteries last 4 , 5 years. Cheap walmart everstart batteries.

 

[Jahee]

Went to get the battery tested today, it was reading as "Unservicable"..

Bought a new one for £37 and everything seems alright now.. They tried charging me £15 to fit it! Hah!

 

[boomerang]

Glad to hear it was something simple!

 

[LTC8K6]

Good to hear it was not a more expensive part.

Is that British for "does not work"?

 

[Jahee]

Originally posted by: LTC8K6
Good to hear it was not a more expensive part.

Is that British for "does not work"?

Haha, god knows, the chick that tested the battery tried to enter it as 16Ah, when infact its 44Ah.. Which of course read as a perfectly fine battery :roll:

She was saying to me, "Well, the battery seems fine! Its registering as 92%.." and when i said 92% of what she kind of gave me a look! She was actually looking at the 160CCA number and entered that as 16Ah into the tool.. I bit my tongue she was only young!

 

[imported_Truenofan]

I'm going to disagree.

The alternator's current output is low at idle and it does increase with RPM.

thats a generator. they have those on our HMMWV. those increase power per rpm. but they also have an external voltage regulator on them as well to make sure they don't go over a certain voltage... and even at idle, they generate enough power. my car has a voltage meter, its quite accurate as to if my alternator dies, and i drop below a certain level. unserviceable is any language for not working. we use it a lot in the military though. there's serviceable which means its ok for duty, and unserviceable which means you cannot use it...

 

[Thump553]

Originally posted by: steppinthrax

Originally posted by: Thump553
Three and a half year old battery is pretty old these days, cars put a whole lot more demand on the electrical system than they used to.

It's the beginning of cold weather season, I'd either break down and buy a new battery now or be prepared to walk/shiver/be late.

I've had batteries last 4 , 5 years. Cheap walmart everstart batteries.

I had pretty good experience with those Walmart Everstarts. I'm not sure if any of my replacements have been in as long as four-five years (yet), but they seem to last much longer than the batteries supplied with cars these days. I've had to replace the original batteries at 2-3 years more likely than not.

 

[LTC8K6]

thats a generator. they have those on our HMMWV. those increase power per rpm. but they also have an external voltage regulator on them as well to make sure they don't go over a certain voltage... and even at idle, they generate enough power. my car has a voltage meter, its quite accurate as to if my alternator dies, and i drop below a certain level. unserviceable is any language for not working. we use it a lot in the military though. there's serviceable which means its ok for duty, and unserviceable which means you cannot use it...

No, it's an alternator and voltage does not equal current. When you test an alternator's current output, you hold the engine at 2,000 or 2,500 rpm.

There is an idle output spec and a maximum output spec.

As the load on the alternator increases, it gets harder and harder to turn the alternator.

I know what unserviceable means.
I know what NMC means, too.

 

[jagec]

Originally posted by: Truenofan

I'm going to disagree.

The alternator's current output is low at idle and it does increase with RPM.

thats a generator. they have those on our HMMWV. those increase power per rpm. but they also have an external voltage regulator on them as well to make sure they don't go over a certain voltage... and even at idle, they generate enough power. my car has a voltage meter, its quite accurate as to if my alternator dies, and i drop below a certain level. unserviceable is any language for not working. we use it a lot in the military though. there's serviceable which means its ok for duty, and unserviceable which means you cannot use it...

Wrong.

The old-fashioned generators that they used to use on gasoline engines used reduction gears to slow down their RPMs relative to the engine, and they generated practically nothing below a certain RPM. Once the RPMs got up there, they would start to output the DC, but they weren't very rugged and were somewhat complex.

Alternators actually use a smaller pulley to spin FASTER than the engine, which increases power output at low RPMs. Power output still scales with RPM, it just has a lower threshold to produce useful current. A set of rectifiers is necessary to convert the output of an alternator to psuedo-DC.

 

[imported_Truenofan]

http://en.wikipedia.org/wiki/A...Automotive_alternators they stay at the same voltage, and amps. an automotive alternator, which is what we're talking about, does not increase anything as engine rpms go up.
http://en.wikipedia.org/wiki/Electrical_generator they were used in vehicles, but were unreliable, and require a battery to keep voltage steady.

there's a reason for pulley sizes. and why you don't put something that requires torque to drive, on a regular gasoline engine. you put it on something that can supply the torque needed, like a diesel engine that revs low and supplies lots of torque across the whole band.

 

[LTC8K6]

"an automotive alternator, which is what we're talking about, does not increase anything as engine rpms go up."

You can repeat it all you wish, it won't make it true. The line below, from your wiki link, proves it's not true. A bigger pulley would rotate the alternator slower, reducing it's output, because the current output of an alternator varies with RPM.

"The stronger construction of automotive alternators allows them to use a smaller pulley so as to turn twice as fast as the engine, improving output when the engine is idling."

A typical alternator output chart:

http://www.prestolite.com/imag...-4900_185Amp_curve.pdf