All-in-all, a very nice post, Rick. However, the part I bolded above is the bit I have trouble with. I fail to see how a slow discharge is significantly different than a battery with at least a significant fraction of a full charge sitting on a shelf, self discharging. Although the self-dishcarge rate is very low (on the order of a few milliamps, IIRC), even a much larger (but still “slow”) discharge, say a few hundred mA won’t cause much in the way of measurable heating or anything else that I can think of that would cause the sulphation to harden. Batteries can sit, charged, on the shelf for a few years, and AFAIK, the sulphation doesn’t begin to harden until the level of discharge becomes severe. Can you explain the mechanism by which a slow discharge causes the hardening? I’ve always taken the sulphation hardening to be caused by the amount of sulphation more than the time the sulphation is allowed to sit. Otherwise, new batteries which sit on the shelf for several months before being purchased would be almost worthless.
My experience is that battery manufacturers rotate their vendors stock so that no batteries are on the shelf for more than three months. The old (longer than 3 months) batteries are reclaimed or refurbished at the plant. Where are you finding batteries that sit for years and are still offered for sale?
Can anyone explain why the jump-starting attempts wouldn’t have worked, if the battery was still rechargeable?
Yeah, now that you mention it, what about that?
It happened the first time too, which is one reason I bought a new battery. I figured I had killed the old one.
Q.E.D. thanks for the compliment.
Now as far as the thick /thin vs hard soft discussion goes, at first I thought you might have a point with the thickness of the PbSO4, but its thickness would be the same regardless of if the headlights were left on all night or the car was parked with a 25mA draw for 3-4 months. I can tell you from experience that if you left the headlights on all night, the battery (all other factors being equal) will soak up the chargre like a sponge. The car that got its dead battery from parasetic draw will only take a very low current over a very long time. To try and fast charge it will cause the voltage to spike, heat and gas to be generated. So I can’t go with the thick/thin theory. In the industry the term sulphation is used to describe a battery that is discharged and either will not take a charge at all, or only take a very low charge current. That battery charger I mentioned in my last post is a 5A charger. [mini rant] Most commerical battery chargers are sold for the wrong reasons, and with the wrong abilities. When you go to a tool truck, or a store and they have a new charger, if you ask about it the response is always the same “This bad boy puts out 600A!” This is the booster setting and in no way represents the best way, or for that matter any way to charge a battery. Trying to charge any automotive battery @ 600A would destroy it. [/mr]
I can’t speak for other people that sell batteries, but my company requires a test and re-charge on any battery that sits on the shelf for more than 6 months. Places that sell lots and lots of batteries like Sears get weekly battery deliveries and carry a 1 month supply at the most. For small repair shops*, and odd size batteries that sell very slowly, the batteries are shipped dry, and eletrolyte is added when the battery is sold.
*Interstate batteries (and other compies like this) will put batteries in a shop on consignment basis, and rotate the stock every few months.
I will ask a few of the really smart guys around the company and see if I can get you a better answer.
Because alternators are not battery chargers. Even though the alternator in your car might be rated at 150A or more (the alternator in my car is rated at 180A, and will put out almost 200A 
) the control circuit is designed to supply the car’s electrical demand, and act as a trickle charger for the battery itself. if you read up to Crafter Man’s post it can take days to trickle charge a battery. You probably would not / could not drive long enough to charge a dead battery using the alternator. Alternators and the voltage regulators are designed to keep a fully charged battery fully charged, and bring up to a full charge an almost fully charged battery.
True story, customer buys a new car in Santa Monica. When picking up the car, it won’t start (sat on the lot too long and had a dead battery) Salesman jump starts car and says you live a long ways off, the alternator will charge the battery. Customer drives off to Apple Valley (Way the hell out in BFE, over a 100 mile drive from dealer) gets there, goes to take wife for a drive in his new car. Guess what? it won’t start, battery is dead. Not 100% dead, but no where close to starting the car. He calls for a tow, and they bring the car to me. I replace the battery and all is fine and good.
Bottom line, alternators do a different job than a battery charger.
Rick, I think you’ve misunderstood my use of “jump start.” I didn’t mean rolling it and popping the clutch. (I’d call that bump starting, not jump starting.) I meant using jumper cables from another car.
Both times this happened, I tried jumping from another car, whose engine was running, and the car with the dead battery still wouldn’t start. In the most recent case, I tried to jump from two different cars, just in case. It would crank once, and then stop, lights out.
I don’t get why, when I’ve got a good battery (in car B) in parallel with the bad one (in car A), the good battery shouldn’t start car A, regardless of the condition of the bad battery. Presumably, if I had removed the bad battery from the circuit, car B’s battery would have started car A. But the dead battery somehow prevents this.
I wouldn’t call it a trickle charger. If the battery is low, and there aren’t many accessories running, the alternator is capable of pumping quite a few electrons into the battery over a short period of time. The amount of current going into the battery will depend on the battery’s V[sub]oc[/sub], the maximum current output of the alternator, and other loads connected to the alternator.
Neither would I. How you got ME quoted for something Rick posted is beyond me. Unless you did it manually and had a brain fart. 
Crafter man from your link
I stand by my comment that an alternator is not designed to charge a dead battery, but rather to keep a fully charged battery fully charged.
Oh by the way on that 180A alternator on my car? It produces 50A at idle when requested by the voltage regulator. So at some point you gotta ask, how does Rick know this? Simple when I am teaching starting and charging systems we test he output under various conditions. We attach a amp meter and a carbon pile load to the car start and let idle. At idle we increase the load until the voltage drops to 12.7 (max A output) and read the result. about 50A at idle. I would never expect to see 50 if I just hooked up an amp meter, regardless of the condition of the battery. Why? The control circuit in the voltage regulator. A lot more sophisticated then the days of yore. Hell some of our cars now have computer control of alternator output voltage. So what a system can do, and what it does do may be two different things.
commasense Yes I did misunderstand you, sorry about that. Jumper cables come in many flavors from complete shit for less than $10. to very good for over $50. If your battery had almost enough power to start your car (car cranked slowly, but it did crank) a cheapo set might and I repeat might do the trick. If your battery is left the headlights on all night, stone dead even the really good sets of jumper cables might have to stay attached for a couple of minutes to pump enough amps over into the dead battery to have a chance.
To give you an idea of price varrations I paid about $50 bucks 20 years ago for my set of jumper cables.
**Q.E.D.**Neiner, neiner, neiner. My post got mistaken for one by Q.E.D. Woot!
Yipes, how did that happen? :smack:
Rick:
I was simply responding to the statement, “the alternator acts as a trickle charger for the battery itself.” I guess when I see the term “trickle charger” I think of something that produces a fairly low current (around 1 A or less). Perhaps this is incorrect.
We’re in agreement that an automobile’s charging system is not designed to fully recharge a dead battery is a short period of time.
Crafter Man I don’t think we are as far apart on this as it may seem. My use of trickle charger is maybe a bit over the top, but when dealing with students that are sometimes aah shall we say thick as a brick, someitmes you tend to resort to hyperbole.
Let me try and clear this up, just a bit. When dealing with a fully charged or almost fully charged battery, the alternator will put out a ton of juice to recharge the battery in short order. However when dealing with a flat battery, the alternator will only allow a few amps at a time into the battery hence my trickle charger comment.