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Old 01-21-2004, 08:12 PM
bingowah bingowah is offline
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Car battery dead (it seems) but charger shows as full?

Okay please pardon me if this seems OT but I'm genuinely curious right now about the science behind it and the reasoning why, if this is the case. I have a 1977 300D Mercedes I recently acquired, I didn't drive it at all over over a month because of the winter conditions. Yesterday I went to try to start it and it chugged a bit and then the lights started dimming, the engine not starting sucessfully. I'm reasoning this is because the battery is dead -- there hasn't been any other wear and tear on it recently, for that matter, too. I don't think it is a corroded battery because I don't see any white powder or anything there...

I'm not a big car buff, but is it likely the battery (an Interstate Mega-Tron Plus 93 drained because I didn't drive it for that period of time? Is that the logical explanation? Anyhoo...

Okay, so I go to charge the battery, doing basically the same thing with my battery charger with cable clamps that I did to a minivan a little while ago, and successfully charged that minivan (and with the minivan, the charger's indicator showed that it in fact was empty and moving slowly towards full over the course of many hours).

But with this car, the battery shows up as FULL on the diagnostic display, the little arrow that points to a little icon of the battery's capacity. Even though I'm quite certain the battery is dead, like I said. I've kept the charger on over a couple hours, and I tried a quick test with the lights... they seem to come on brighter, but barely so... could just be my imagination as it gets darker outside. But I'm stumped now. I don't want to damage things or make things worse by overcharging, but on the other hand, I'm going to need to drive this car soon. The charger (it is a Motomaster) doesn't feel very warm... should it be? I don't recall what it felt like when I used it with the minivan.

What could this possibly mean?
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  #2  
Old 01-21-2004, 08:20 PM
Oat1957 Oat1957 is offline
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Check the battery with a volt meter. Put the leads where the cables connect on the battery. Red on the +(positive) and black on the -(negative).

It will read 12 VDC when the battery is charged and the engine is off.
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Old 01-21-2004, 08:21 PM
Eleusis Eleusis is offline
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Quote:
What could this possibly mean?
It could mean that the cables aren't tight enough.
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Old 01-21-2004, 08:23 PM
Oat1957 Oat1957 is offline
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Or it could mean the connections need to be cleaned.
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Old 01-21-2004, 08:24 PM
Q.E.D. Q.E.D. is offline
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Quote:
Originally Posted by Oat1957
Check the battery with a volt meter. Put the leads where the cables connect on the battery. Red on the +(positive) and black on the -(negative).

It will read 12 VDC when the battery is charged and the engine is off.
Unfortunately, this tells you nothing of the condition of the battery. I've seen batteries with almost no capacity at all reading 12-14 VDC. IOf the battery is still not strong enough to start the engine, it needs replacing, regardless of what a voltmeter tells you.
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  #6  
Old 01-21-2004, 08:46 PM
Patty O'Furniture Patty O'Furniture is offline
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You need to measure the battery's terminal voltage under load. This means while the engine is cranking. It's possible to read nearly the fully rated terminal voltage on a dead cell if you take a no-load measurement. This is due to the battery's internal resistance and the loading effect of the measuring device (the theory behind this is complicated and I won't attempt to get into it here).

A battery charger normally does get warm when it's working, unless it's a very slow trickle-charge type. The easiest thing would be to simply get a set of jumper cables and see if the car will start off of a working alternator in another car.
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Old 01-21-2004, 08:50 PM
BubbaDog BubbaDog is offline
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A battery can fail in a number of ways. It's possible that yours is dead but I really can't tell from here.

Voltage and current are the two terms associated with electricity. As an analogy think of voltage as the highth of a waterfall. Current is the amount of water going over the waterfall. So you can have a 12 foot waterfall that has one gallon of current but you could also have one that has 50 galloons of current.

Usually when a battery fails and you put a charger on it the charger will supply current to the battery. The amount of current leaving the charger is measured by the charger and reported to you. When lots of current leaves the charger it reports that your battery is low. As the battery charges it builds up a resistance to the current, the amount of current decreases and the charger tells you that the battery is fully charged. So the battery charger doesn't really know when your battery is charged it just knows when current is no longer leaving the charger.

If you have a situation where the charger connectors aren't clamped tight enough or the battery for some reason has resistance to current then the charger will happily and mistakenly tell you that the battery is charged.

You either do not have a good connection from battery to charger or {here's my guess} your batter is charged and you don't have a good connection between the battery and the car's starter.

I suspect that you might get the car started if you tighten the battery cable connection.

Bubba
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  #8  
Old 01-21-2004, 09:02 PM
bingowah bingowah is offline
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Thanks everyone very much for the info, I'm new at this and really don't know my car stuff so I'm grateful to learn.

Bubba: I believe the screws connecting the battery cables to the car are in very tight, they seem to be that way when I checked them. The car worked fine when I last drove it but I'm suspecting due to this period of inactivity -- that's what made the battery die (hypothetically, if the battery is in fact dead).

The battery in this car is different from the battery in the minivan... so perhaps "resistance to current" is the case?

I just checked again with the minivan BTW and the battery seems to charge and read out fine with it.

Attrayant I'll definitely consider that to try. The battery charger does get warm, but not that much. Hmmm... so you think jump starting is probably a good means of diagnosis? I'll have to figure a way to back the car out the garage then, because I suspect jumper cables well be too short otherwise and I don't want a collision between the side mirrors.

Connections look in good condition -- of course I'm no expert, but they don't seem to be powdery as I've heard (corroded?). Thanks tho Oat1957.

Q.E.D. I'll keep that in mind, thanks for the tip.

Eleusis I would think that, if the car hadn't worked reliably for quite some time and the cables have been tight on that battery for quite awhile I believe. The battery has been in since April 2000.

Hmmmmmm...

Will it still charge even though the charger says it's full? BTW I'm not even quite sure what a voltimeter is, as you can guess I am green at this. But thanks for the info.
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  #9  
Old 01-21-2004, 11:50 PM
Gary T Gary T is online now
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The battery is shot.

The charger indicating a fully charged battery means one of two things: the battery is fully charged, or the battery is faulty and won't take a charge. A battery that has sat for a month and then expended some energy trying to start the engine is not going to be fully charged. It's also unlikely that a connection problem went from symptomless to preventing cranking during a month of sitting. A bad battery is the most plausible explanation for what you've described.

If you want to be 100% certain, have the battery load tested. But if I understand what's written in the OP, it's a pretty sure bet that the battery has failed.
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Old 01-22-2004, 12:06 AM
Rick Rick is offline
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First off Bingowah your OP says that the battery in question is a Interstate Mega tron. In your last post you said it was installed about 45 months ago. According to the Interstate Web site this battery has a 85 month warranty. So assuming that you have the receipt it is covered. Of course this will be a prorated warranty so you won't get a new battery for free, but it won't cost retail.

Now let me give you a little education about batteries. The battery in your minivan is exactly the same as the one in your 300D with one exception. The battery in your Benz has a much larger capacity due to the fact that a diesel require a lot more energy to crank than a gas engine. (And yes they are physically a different size)
Inside of both of those batteries are six cells that produce voltage and current. Each cell when fully charged produces 2.12 volts. Doing the math 6*2.12 gives a voltage of 12.72 Volts for a fully charged battery. industry standard is anything above 12.6 is considered fully charged. As the battery discharges, the voltage drops. A 75% charge is about 12.4 volts, 50% is about 12.2 Volts and if your 12-volt battery reads 12.0 volts it is only about 25% charged. (Sorry about that Oat1957 but you are wrong.)
The problem with trying to determine battery condition with voltage is two fold, first is a condition called surface charge. When a battery is being charged it will show a higher voltage than it should for its state of charge. If you are going HUH? right about now, don't feel bad I have technicians that have problems wrapping their mind around this. Let me explain. Lets say you have a car that has been sitting for a while (2-3 months) you go out to start your car. Knowing that batteries do drain from parasitic draw (electrical draw with the key off. Clock, radio, computers, alarm etc) you decide to check the battery voltage first to see how much charge is in the battery. Let's say the voltage reads 12.0 volts. You get the car started and let it idle for say 5 minutes. If you shut the car off at that point and measure the voltage across the battery terminals it will probably read about 13+ volts. This does not indicate that the battery is fully charged, it indicates that the battery has a surface charge. Left alone the surface charge will disappear in several hours, or you can leave the headlights on for about 30 seconds to remove the surface charge. At this point a voltage reading across the battery terminals would be valid.
Next is the fact that available voltage (and current) falls off big time with cold. I don't have my books here at the house, but IIRC correctly a battery at 0F only has about 50% of the power available at 70F. So if your battery was marginal when the weather was warm (starting the car, but might show up as iffy on a test) it can come up as a dead player when the temp drops.
When batteries go bad they can do so in many different failure modes. One of these modes is that they will refuse to take a charge. This is referred to as sulfation. Sulfation is caused by a battery that sits for a long period of time slowly discharging from parasitic draw. Anyway to make a long story short the battery likes being discharged, and does not want to take a charge at that point. This condition can sometimes be reversed, but usually it is time for a new battery.
I would suggest that you get the car started and take it in to where you bought the battery and get a new battery. If for some reason you cannot get the car started and you decide to remove the battery make damn sure that you disconnect the negative (-) cable first. And whatever you do, do not let the wrench bridge between the positive and negative cable ends. The battery may not have enough power to start the car, but if you short it, you will be very surprised at how much power is left in the battery.
When installing a battery always connect the positive cable first and then the negative last.
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  #11  
Old 01-22-2004, 12:11 AM
Rick Rick is offline
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Quote:
Originally Posted by Gary T
The battery is shot.

The charger indicating a fully charged battery means one of two things: the battery is fully charged, or the battery is faulty and won't take a charge. A battery that has sat for a month and then expended some energy trying to start the engine is not going to be fully charged. It's also unlikely that a connection problem went from symptomless to preventing cranking during a month of sitting. A bad battery is the most plausible explanation for what you've described.

If you want to be 100% certain, have the battery load tested. But if I understand what's written in the OP, it's a pretty sure bet that the battery has failed.
Figures, while I am writting the great opus on life the universe and batteries, Gary T comes in and answers the OP in four words.
Quote:
The battery is shot
Short, sweet, to the point, and almost without a doubt correct.
I gotta learn not to be so long winded.
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Old 01-22-2004, 08:44 AM
bingowah bingowah is offline
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Thanks for all the info everyone... I've learned a lot here. Thanks Gary T for your conclusion and reasoning behind that, I'm beginning to think these are the signs of a shot battery.

Rick... wow are you a car expert or what!! That's some education alright. I didn't know all of that stuff! I'm alright at math and although it's beginning to do my head in, but it makes sense to me with your explanation about the voltage. So cold DOES have a huge effect... I didn't think that'd be the case, as I used to store small AA batteries and such in the freezer (I now know this is likely an urban legend of sorts and not terribly effective) and I wasn't thinking about that "sulfation", the draining about it. Ouch.

No, I really appreciate the long and the short of it. Tremendously. Thanks a LOT for the safety warning too, I'm spooked about things like that and was surprised once at the shower of sparks that came out of a friend's car after a jumper cable session gone bad.

Positive first, Negative last! I'll remember that. THANKS A LOT AGAIN

This is an amazing place to be and you guys are so knowledgeable.
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Old 01-22-2004, 08:45 AM
BubbaDog BubbaDog is offline
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Rick
I would expect a battery that failed open (doesn't take a charge) would also show no voltage and not be able to operate the headlights.
But heck, without looking at it, I just can't make a definate call.

Bubba
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Old 01-22-2004, 08:54 AM
bizzwire bizzwire is offline
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No expert here, but would it be worthwhile taking the battery out of the car, bringing it inside the house to warm up, then reinstalling it?
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  #15  
Old 01-22-2004, 09:08 AM
Gary T Gary T is online now
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Quote:
Originally Posted by bingowah
So cold DOES have a huge effect... I didn't think that'd be the case, as I used to store small AA batteries and such in the freezer (I now know this is likely an urban legend of sorts and not terribly effective)....
No, you've got apples and oranges here. Cold has a detrimental effect on a battery's efficiency, and not as much power is available in USING a battery when it's cold. However, cold has a helpful effect on a battery's shelf life, which can be lengthened by STORING a battery in the cold. Just let it warm up before using it.
Quote:
Positive first, Negative last! I'll remember that.
Please remember that that's the sequence for RECONNECTING. The sequence for DISCONNECTING is negative first, then positive. The point is you don't want the negative still connected when you're working on the positive connection.
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Old 01-22-2004, 09:14 AM
Gary T Gary T is online now
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Quote:
Originally Posted by BubbaDog
I would expect a battery that failed open (doesn't take a charge) would also show no voltage and not be able to operate the headlights.
Not taking a charge doesn't usually equate to having an open circuit. There's a world of difference between the power required to light the headlamps and the power required to crank the starter. For a battery to be capable of the former and incapable of the latter is not unusual.
Quote:
But heck, without looking at it, I just can't make a definate call.
Yes, there are limitations to what we can do over the phone or on the 'net. Not the same as being there with our tools and test equipment.
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Old 01-22-2004, 09:19 AM
Gary T Gary T is online now
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Quote:
Originally Posted by bizzwire
No expert here, but would it be worthwhile taking the battery out of the car, bringing it inside the house to warm up, then reinstalling it?
In some cases, that could be helpful. But if that battery showed fully charged on the charger's indicator the moment the charger was connected, it has a bigger problem than just being cold.
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Old 01-22-2004, 10:36 AM
Kreekurmudgeon Kreekurmudgeon is offline
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Thanks be unto Rick for that comprehensive and accurate reply. The only thing I can think of to add is a point that does not seem to apply in this instance since the OP said the battery had only been out of service for about a month.

It's a little known fact that the electrolyte in a battery will settle out (separate) if a battery is stored for a long period of time, say six months or more. The problem can be corrected simply by shaking hell out of the battery, or by riding it around in another vehicle for a day or so.

For those who might say I don't know what I'm talking about, try it before you condemn. Store a fully-charged battery for a year, then get before and after voltage and load-test readings.
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Old 01-22-2004, 10:42 AM
zwede zwede is offline
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Several excellent posts about the physics of batteries in this thread. Yes, a battery can definitely fail in a way that it will not take a charge. As a matter of fact I had that happen about 2 years ago. The battery was very old at the time (over 6 years) and the car was at a body shop after a pickup ran into me while I was stopped at a stop sign. The car sat at the shop for about 2 months and then wouldn't start. They got it jumped and I drove it home. During this time the voltmeter kept showing an unusually low voltage (between 11 and 12V, instead of 13.5-14.5).

When I got home I hooked up the charger and the battery would not take a charge, and the engine wouldn't start. A new battery fixed it right up.

Your diesel puts much more stress on the battery as the high compression of a diesel means your starter motor needs more current than the starter for a gasoline engine. Add to that the cold temperatures and you see that you need a battery in tip-top shape to start.
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Old 01-22-2004, 01:55 PM
Rick Rick is offline
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Quote:
Originally Posted by Kreekurmudgeon
Thanks be unto Rick for that comprehensive and accurate reply. The only thing I can think of to add is a point that does not seem to apply in this instance since the OP said the battery had only been out of service for about a month.
The battery could have been failing for several months or more. The one month storage was just the nail in the coffin. I have tested batteries that test right on the very edge of bad. yet they started the car fine and continued to do so for several months when used in daily service. If that battery had been left in the car unused for say month it probably would have been DOA when it came to start the car.

Quote:
It's a little known fact that the electrolyte in a battery will settle out (separate) if a battery is stored for a long period of time, say six months or more. The problem can be corrected simply by shaking hell out of the battery, or by riding it around in another vehicle for a day or so.

For those who might say I don't know what I'm talking about, try it before you condemn. Store a fully-charged battery for a year, then get before and after voltage and load-test readings.
I'm not to sure about this. I have cars that I leave in remote training centers for months and months at a time, and I do not have a problem when it comes time to use the cars again. Do you have a cite for this?
The one precaution I always do is I charge the battery fully before leaving and then disconnect the negative cable. I think the longest I have gone is 6 months with no ill effects.
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Old 01-23-2004, 03:04 AM
bingowah bingowah is offline
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Thanks for the clarification Gary T, I definitely had that one mixed up.

This is shaping to be a really informational thread. It's cold right now but not tremendously so, maybe -3 Celcius.
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  #22  
Old 01-23-2004, 04:13 AM
Quint Essence Quint Essence is offline
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battery terminals WILL corrode no matter how tight your connections seem or how long it has worked with no problems.
Use a wire brush and clean the terminals and the posts and see if it makes a difference. If it doesnt then likely you will need a new battery.
If the car started (i wasnt entirely clear on that from your post) and THEN the lights began to dim and the power failed, then your problem is not with the battery but rather with the alternator.
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