Originally posted by: brblx
please don't condescend to me. yes, current turns the starter, that's exactly why you don't say that a battery is defective because it doesn't show 12.6v. despite what you may have read somewhere, you cannot accurately judge state of charge by battery voltage. ambient temp and the condition of the electrolyte both have an effect on what voltage will be produced. not to mention the typical presence of a surface charge. it's a guess, at best.
Despite what you think you know, a battery that shows 12.2 volts at rest is indeed severely discharged. I agree that it may not be completely bad, but the probability lies in that direction if it has stayed at that level of charge for any significant length of time. Sulfation starts at 12.4 volts and below and it's quite likely that a battery that has been sitting at 12.2 volts for a decent amount of time will load test at significantly less than rated capacity.
A surface charge dissipates within a few hours of a battery coming off a charger. I sincerely doubt that the OP had the battery on a charger immediately before he checked the voltage. In any case, a surface charge causes an artificially
high voltage reading. If a surface charge were causing the 12.2 volt reading, then the battery would be in even worse condition.
The fact is that the OP is in Michigan and was testing the battery on a summer day. It's not even close to cold enough to cause a low voltage reading from temperature.
Yes, electrolyte condition can affect voltage; electrolyte condition affects
every aspect of a battery's electrical performance. And guess what? If the electrolyte is bad, the battery needs to be replaced! Shocking!
Originally posted by: brblx
beyond that, having a 50% charge is unlikely to have ANY effect on cranking. perhaps your electrical genius has forgotten that it is voltage that pushes electrons, not current. being down a few tenths of a volt is not going to magically inhibit the battery from pushing current through a wire, and at 50% charge it would still have plenty of reserve capacity left- if it took 100% of the charge in a battery to turn a starter a few times, we'd all be screwed. why do you think a starter spins at approximately the same speed whether the battery has 100% charge or a 25% charge? it's not until the battery begins to become utterly spent that you'll get the familiar slow lugging of the starter.
So much wrong. Voltage is indeed roughly analogous to "pressure" and it is indeed what causes electrons to flow. However, current draw is king. 20,000 volts at 0.000001 amp is equivalent to a shock from "static electricity"; it's incredibly high voltage but there aren't even close to enough amps to power anything. Similarly, if a battery is at 50% charge, it's ability to deliver amps is also impaired. While the voltage difference between a 100% charge and a 50% charge is inconsequential for most regulated electronics, the amperage difference between a 100% charge and a 50% charge is most certainly enough to factor into starting performance given that a loaded starter on a V8 engine can draw 200-300 amps while under load.
Automotive SLI (Starter, Lights, Ignition) batteries are designed to operate for their entire lives between 80% and 100% charged. They are not designed to be used at a 50% SoC.
Originally posted by: brblx
and to say that a discharged battery is not only his problem but is due to a fault in the battery itself is just silly.
When one hears hoofbeats, it is best to think "horse" and not "zebra".
Originally posted by: brblx
as i said, the only time voltage is a clear indicator of a bad battery is when it's down ~2.1v due to a bad cell. and even then, that's not a sure thing- i've charged batteries that had 10v or less and had them come back to life (though the deep cycling is obviously not good for them). the only way to really be sure is to fully charge the battery (if possible), put a load on it with a carbon pile, and look at the voltage drop. conductance testers will work, as well, but can, on occasion, both condemn a good battery and let a bad one slip by.
he can feel free to put a new battery in as cheap insurance. but it's not causing his no-start, and it's just as likely that a weak alternator or corroded cable/connection is to blame for his low voltage. if he's going to go with the blind shotgun method, he might as well replace the rest of his starting and charging system, too. or he could just drive the truck, and if it happens again, troubleshoot the problem properly, now knowing that the starter motor itself is likely fine.
A weak alternator would show up through a MIL (Malfunction Indicator Light) unless something absurdly uncommon is going wrong. Again, when you hear hoofbeats, think "horse" and not "zebra". Yes, it's possible that there are other factors in play, but 99 times out of a hundred when the battery shows low voltage at rest and is over 3 years old, it's the battery.
Originally posted by: brblx
edit- for the record, i'm not trying to be complete ass, but it's aggravating to be talked down to just because i recommended he actually look for the problem and not just replace the first iffy thing he sees, especially when it's obviously doing the job right now.
Put on your big girl panties and deal with it. I'm not going to recommend overkill just so you'll think I'm a nice guy.
Yes, if continued issues present themselves he will need to trouble-shoot the charging system and his cables/wiring, but all the probability lies in the direction of the battery being at fault. After living through 3+ Michigan winters and summers, the odds are that it's just tired and old. It's ridiculous to recommend that he spend hours diagnosing an intermittent electrical issue when such an issue is just not the probable cause.
Originally posted by: brblx
i would say that a connection is probably to blame, but it seems odd that the starter worked fine for months before acting up.
Electrical connections are like that. I worked on a '92 Corolla that worked perfectly every day until one morning it refused to start; wouldn't even accept a jump start. Battery tested fine. No corrosion on the terminals or on the starter. Every single connection looked fine, but no matter what was done, the car would just not start, despite working perfectly right up until the morning it stopped starting. I took apart the positive battery cable (which contained a small maxi fuse block); again everything looked fine, continuity test was good, maxi fuses were fine. Still no start. Out of desperation, I got a wire wheel and just cleaned every connection I could find, even if it looked perfect.
Car started immediately and ran perfectly thereafter.
Sometimes a connection just stops working even though it looks fine and worked perfectly just a day before.
ZV
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