voltage low on car battery

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snipped-for-privacy@snyder.on.ca wrote:

You just said it was "an open or high resistance cell." I thought by "high resistance" you meant a slow internal drain.

It's easy if you read the numbers on the meter. If you have one shorted cell, you'll see about 10.5V.

You've introduced the concept of partial shorting. They're all like that. I believe a new conventional lead-acid battery on the shelf will drain in a month or so at room temperature. (Maintenance-free batteries drain more slowly.) New batteries have "partial shorts" and most work fine.
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wrote:

If you nhave a totally dead battery you will too, or if you have several partly shorted cells. But you are right, GENERALLY a battery that is down roughly 2 volts AND STILL CRANKS AN ENGINE has a shorted cell.

No, new batteries do not have "partial shorts" they have self discharge, which is "normal" but it won't drain in a month. A GOOD lead acid battery will hold about 80% charge for 6 months. A "pure lead" battery = no calcium or antimony, will hold a LOT longer than that. A Hawker Genesis EP has a "shelf life" of almost 3 years.
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snipped-for-privacy@snyder.on.ca wrote:

A totally dead battery won't show 10.5V with the lights on.
What would be the point of trying to crank the engine? If five good cells cranked it one day, they might not do it the next. Under a big load, they could produce less than 8V.

All batteries have electrical leakage within the cells.
which is "normal" but it won't drain in a month. A GOOD

On the shelf, a typical car battery will be down to 80% in 12 days at 100F, 30 days at 80F, and 100 days at 50F. A particular model may discharge faster or slower.

That's lead-tin stored at a cool temperature. Are they practical?
Car manufacturers use batteries intended to start the vehicle after two weeks parked. If you disconnect the battery, the time you can park and still get started varies from 1 to 6 months, depending on the temperature and the model of battery.
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On Wed, 4 Feb 2009 04:54:17 -0800 (PST), ransley

Charging voltage and fully charged voltage are NOT the same. Charging voltage can be as high as 14.6 volts, which can leave a surface charge of 12.9, +/- for a short time after charging, but a FULLY CHARGED Lead Acid battery is 2.1 volts per cell ( so 12.6 volts). It takes 2.15 volts per cell to START to charge the average lead acid battery, so anything less than 12.9 volts is not charging at all.
13.8 volts is the "recommended" maximum charging voltage according to most manufacturers.
Best way to check BATTERY voltage is to turn on the headlights for 2 or 3 minutes, then turn of the lights and check the voltage.
Checking with the headlights on and comparing the voltage will give an indication of the batterie's internal resistance.

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mm wrote:

The battery behaves pretty well. I haven't bothered to check cranking voltage because it sounds good. It's in a van belonging to a couple who are away most of the time. I've been charging it occasionally because extended sitting without charging harms batteries. A few weeks ago they were about to replace the battery because the van wouldn't start, but I found resistance at the positive terminal connection.

I checked the meter on a battery that I'd charged two days before. 12.6.
In that connection, I had switched to 10A to check the charging current. Then I checked voltage across the terminals. Zero... uh-oh, the plugs were in the 10A jacks. I've damaged meters that way before, and I never learn. This time there was no arc. At home, I checked it on a 5A source and got a good reading. Could my cheap DMM have circuit protection on the 10A inputs? I need to take it apart and see!

The water level is good. As I don't know where the battery came from, I don't know what it was filled with.
Decades ago, I got a manual a major manufacturer had published for dealers. It said that a battery sold in Toronto may have a stronger electrolyte than one sold in Miami. Higher acid concentrations help in cold weather but shorten battery life in hot weather.
I think some batteries are shipped dry, and the dealer adds a mixture of distilled water and acid drawn from a bulk container. Suppose the dealer used a mixture 30% too weak, perhaps for longer hot-weather life or because he didn't have enough acid or because he wasn't good at measuring. I wonder if that could cause the effect I see.
If the battery has sulfation too hard for the charger to break down, I guess that, too, could keep the battery from charging fully.
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all batteries today are wet charge, time in transit before sales are short and warranties long
there are definetely differences, batterys for hot place like phoenix and cold places like canada,
final test is capacity checked by load test.,
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wrote:

Then I wouldn't worry too much. Especially if they are not there much, now is no time to buy a new battery. It depends on their personalities and how much money they have. I at least would rather have a crummy battery and buy a new one only when i was home, using it every day or two, and actually having trouble starting.

Between the battery cable and the positive post? Certainly possible. Clean it off with baking soda and water. Once I was in a hurry, taking a friend to catch his train back to NYC. The car stalled at a red light something was so bad. I touched the battery posts and one was burning hot. That's not the powerful post, it's the bad connection. Put on a glove and I just twisted the cable back and forth until I got a better connection. After I dropped my friend at the train station, I took the cable off and cleaned it and the post with a two-endded battery brush. The connection was so bad, I couldn't even chargethe battery from the car. (I had been having a bit of trouble but didn't identify it until on the way to the train station.)

OK. Well 12.3 is's low.

That's strange. You probably blew a fuse. Even some cheap ones have a fuse.
You can also replace the resistor if you burned out one of those. If you can't determine what the resistance shoucl be, often there is apattern, 2 ohms 20, 200, 2k, 20K, 200k, 2Meg. Or maybe 5.1 etc. Plus maybe you can find the schematic.

Maybe. It might even have what's it called, that lets the current go ahrough when the voltage is high enough.
More below

Absolutely Delco advertised for decades that its batteries were dry-charged, shipped without acid. I think that means they don't discharge or age in any way when they sit on the shelf in the warehouse or the store. Maybe they don't do that anymore, but the motorcycle I bought 2 years ago was like that. It came with a plastic bag/box of acid for me to add.

Could that actually happen? I always thought the acid was pre-mixed. It certainly was with the motorcycle battery I bought. I am opposed to shipping water around (like the pre-mixed windshield washer fluid) but no6 in this case.

Slow charging, with a 1-amp charger, works best, but takes over 24 hours to charge a fully discharged battery. Now that I have a job, I'm happy to use my 10 amp max charger, which puts enough in to start the car after 10 minutes. After the car started, I used to then keep the heater fan on high (which uses a lot more current than headlights do, and is actually sufficient to lower the charging rate) while I drove, so that the battery would charge more slowly. Now that the stupid new cars don't even have ammeters, and the thrill of installing one only lasted me through one car, I don't even bother. It doesn't really seem to have shortened my battery life. I still get 5 years, and I had never been able to get more than that anyhow.
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Years ago I bought a professional charger with 200 amp boost. it works awesome good. will start a stone dead battery
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mm wrote:

I opened the meter. It's about 40mm of wire, about 12 gage, between the 10A and Common terminals. No sign that it has been hot. On meters I've damaged, the only visible sign was discoloration of the wire, but they would no longer give consistent amp readings.

It's a cheap meter. I've often had to use contact cleaner to get continuity at the input jacks. My theory is that due to invisible corrosion, the contact patch between the test-lead plug and the jack was so small that when the battery surge hit, it immediately overheated, breaking contact and protecting the meter. What luck! Cheap stuff works best!

I have another theory now. Whenever you start an engine with a battery that's not fully charged, you may pop sulfate off the plates. Batteries have room at the bottom where it can settle without causing electrical leakage between plates. The sulfate that pops off is lead and acid that can't be recovered by charging.
I'll bet that battery has been used countless times to start when not well charged. I'll bet sulfate at the bottom of the battery accounts for my inability to charge it above 12.3V. (About 60%?)
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wrote:

That is what is known as a "shorted" cell. And it is not sulphate, necessarily. It is "active material" which is spongy lead and lead oxide.. When a battery is dead, both plates are basically lead sulphate (pbS04) and the electrolyte is basically water. Fully charged the electrolyte absorbs the sulphate, becoming H2S04 leaving one plate pb and the other pb02.
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wrote:

Poly-fuses are getting pretty cheap these days and are used for a lot of those applications. It's like a conductive wax thet melts when it gets hot - and doesn't conduct when melted, but when it cools it reforms and conducts again.
That is NOT the exact explanation of how it works. Note I said it is LIKE - so don't bother flamong me if you happen to be an electronics wizzard.

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wrote:

If you are looking for the smoking gun, you have found it. The battery has not been getting a good charge for who knows how long. The battery, left in a partially discharged state for even a few weeks would have sulfated. That battery may still take a charge, and appear okay, but it has lost CAPACITY. The somewhat low voltage measurements after charging indicate exactly that.
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For more than you probably want to know about batteries:
http://www.batteryfaq.org
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Rich256 wrote:

Thanks, it looks like a gold mine.
I see you can expect 1000 starts if your battery is typically at 60% charge and 13,000 starts if it stays at 100%. That's why I made a panel meter to alert me when my battery needs topping off.
I'll see if the site leads me to a chemical explanation of why voltage works as an indicator of the state of charge.
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wrote:

That's simple - the electrical potential difference between dislike materials. Lead to lead oxide is 2.15 volts, more or less. Between lead sulphate and lead sulphate is 0 volts. The percentage concentration of lead sulphate difference between the plates indicates the level of charge and the potential difference between the plates.
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snipped-for-privacy@snyder.on.ca wrote:

Why does the acid concentration change the 2.15V between lead and lead oxide? Is there a table somewhere? Does temperature affect it?
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wrote:

Not normally. Normally the water evaporates, especially if there is over charging, and the remedy is to add distilled water until you see the miniscus, the place where the water level rises above the rectangular area and reaches the 1" round tube that extends down from the battery cap.
"Maintenance Free" batteries are supposed to be even less likely to lose water, but I'm sure they still can.
Do you have reason to think electrolyte has been spilled out, then replaced with only water?
How old is the battery and how long the guarantee (which is their best prediction of product-life.)
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Maintenance Free batteries still gas, but at a much lower rate. Most of them will benefit from an electrolyte level check once a year, as most "maintenence free" batteries still have cell covers that you can take off. The manufacturer considers them maintenance free because they usually outlast most of the warranty without needing water added to them. I check mine once a year, and they are usually just a little low and only need a small amount of water.
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wrote:

Unless it has a "lifetime warranty" in which case it is usually good for about 2 years - - - - - -.
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On Tue, 03 Feb 2009 22:30:43 -0500, snipped-for-privacy@snyder.on.ca wrote:

That's the lifetime of white spotted moth, isn't it?
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