Battery Light at Idle

Burt Gummer

Burt Gummer

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Explorer started having the battery light come on intermittently yesterday when at idle. Goes away after a couple seconds, or when accelerating. I checked the battery voltage this morning after sitting all night last night.

12.2 after sitting all night
13.8-14 running.

Seems the alternator is charging, and the car cranked fine. Trying to head this off before the problem gets bigger. Voltage regulator? Battery? Alternator?
 
LeeMajors said:
Last time I had that. Was an alternator on its way out
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That was my first thought, but checking it with the car running its showing right near 14 volts
 
Burt Gummer said:
That was my first thought, but checking it with the car running its showing right near 14 volts
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Thats what mine showed too. Then would spike to 16. Was easier to replace and not worry about sitting on the side of the road. and replacing a battery when it overcharged too long
 
Burt Gummer said:
That was my first thought, but checking it with the car running its showing right near 14 volts
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Its been a few years since I was in the automotive field, so I may be wrong.
I think the alternator on most vehicles has three legs. All legs put out 8 volts max. If one leg is bad it will not put out enough at idle to charge the battery. It will still put out enough at higher rpm.
 
DangerRuss said:
Isn’t 12.2 low if the battery is fully charged? It should be 12.6?
How old is the battery?
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Not quite 3 years. I thought 12.2 was low.
 
12.2 V is indicative of a bad(ish) battery / damaged battery. A fully charged "12V" battery is around 13.6-13.8VDC. You can tell the difference between bad battery and bad alternator (or maybe bad both) using a battery / charging system tester. Best to mosey on down to the local auto parts store that has someone with 3+ brain cells grouped together and ask about a charging system test.
 
Burt Gummer said:
That was my first thought, but checking it with the car running its showing right near 14 volts
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mine would do the same (rev it and it would start charging normally), but the diode and regulator failed upon testing the alternator. id start by load testing the battery (separate from the system), and then test the alternator.
 
12.2 is indicative of less than 50% charge, so it sounds like its not holding. I have not gotten more than 3 years out of a battery in recent history, and have had a few bad ones as well from reputable places, so my vote is to replace the battery. Keep a jump pack with you, and if the problem recurs, swap the alternator.
 
First of all, a bad battery can lead to alternator damage and a bad alternator can lead to battery damage. So it's important to address such issues when they occur and not delay any longer than necessary.

Second, while the electrical system of older cars is pretty simple, some modern cars are a bit more complex due to the needs of the computer systems on the vehicles. A battery may, for example, seem OK in that it cranks the engine fairly strongly, but it may not be able to support the proper voltage requirements for the onboard computer systems at the same time. And the charging systems may be "smarter" than simply an alternator from the days of old.

Third, while alternator output voltage is a pretty good indicator, that alone doesn't mean it's capable of charging the battery properly. A faulty diode can still result in a measured DC output voltage that's "good" (typically 13.5 to 14.5 Volts), but that alone doesn't mean it's capable of providing the required current to charge the battery.

Fourth, 12.2 Volts DC on the battery is a bit low for a fully charged car battery. 12.6 Volts would be normal.

Fifth, sometimes new components don't last, and this includes the battery. My wife had her battery replace and in less than a year it was bad. Not a problem, except for the annoyance, because it was fully covered by the warranty. The same for the alternator. Sometimes the new one will require replacing again. So maintenance history is important.


Sooo....questions:

What year is your Explorer? (Probably not that important...I don't think even the newer Explorers have what I would call a "smart" charging system, but you never know. )

How old is the battery?

What work have you done on this in the past?


Things to do:

- Clean the battery terminals, whether they look like they need it or not.

- Ensure all cable connections are tight...that includes the battery terminals, the ground connection, and the alternator connections. The cables/wiring, clamps, and lugs should all be in good condition, too.

- Check the age of the battery. Battery life is typically 3 to 5 years. If you're in this range, then any suspected battery problem that aren't directly attributable to something else (like a loose connection) is an indicator that the battery should be replaced. If you're beyond 5 years, then you've definitely gotten your money's worth and you're living on borrowed time at this point anyway.

- If your battery seems "weak" at this point when you start the vehicle, then jump it and see what happens. If it starts right up, then the battery is weak, which is either the result of the battery going bad, the alternator being bad, or both.

- At this point, take the vehicle to Auto Zone, Advance, etc. and have them check the battery and alternator with their tester. They should test the battery with the vehicle off, then have you start the vehicle and they'll perform a series of tests to check the alternator. Replace what needs to be replaced accordingly.


LAST WEEKEND:

My wife wanted me to take a look at her sister's car, a 1999 Cherokee, which wouldn't start. Bit of a conversation revealed it was weak when turning over. She didn't know when her battery had last been replaced.

I popped the hood and the positive terminal was crusty with corrosion and the battery clamp covered the installation year on the sticker. I cleaned the terminals, made sure everything was tight, checked battery voltage (12.2 Volts) and got a weak crank. Jumped her battery and it started up fine. Let it run a while during my clean-up, then went out and (because I'm a nice guy) put $20 worth of gas in it (while still running....because I'm not that trusting yet), then did some interstate driving for another 20-30 minutes.

Came back home, shut the vehicle off, and then restarted it with no problems. Shut it off for about 5 minutes, then got a weak crank, but it still started. Battery voltage was back down to 12.2 Volts.

Replaced the battery, problem solved.

Age of the old battery, if you're curious, was 16 years. It had been in her Jeep since 2006! Previously, the most number of years I've ever seen on a car battery was between 7 and 8 years. I was amazed, quite frankly.
 
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Leadchunker said:
Its been a few years since I was in the automotive field, so I may be wrong.
I think the alternator on most vehicles has three legs. All legs put out 8 volts max. If one leg is bad it will not put out enough at idle to charge the battery. It will still put out enough at higher rpm.
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This is my recollection as well. Isn't there a rectifier trio that converts the AC to DC in the alternator? If you lose one portion of the rectifier it will lead to low alternator output at idle.
 
Some other battery information:

I said history is important earlier, and this includes any history of the battery having died before. This is important to know because of how battery chemistry works on lead acid batteries.

If your battery has ever been discharged below a terminal voltage of 10.5 Volts, then the battery has suffered permanent damage, even if you don't notice any problems after recharging.

Battery voltage is produced by the chemical reaction between the sulfuric acid and the positive/negative battery plates. As the battery is discharged, lead sulfate is produced inside the battery. When the battery is recharged, the chemical reaction reverses.

Nominal discharging of the battery does no real harm the battery (other than the fact that capacity will naturally decline over its lifetime of normal use for several reasons). Lead sulfate formed under normal conditions is readily reversable when charging.

However, if the battery is discharged below 10.5 Volts, then lead sulfate crystals form on the plates and this is NOT reversable when charging the battery. (No matter what some battery rejuvination products may claim.) At this point the battery is physically damaged internally and its capacity will be somewhat diminished. How diminished is a factor of how depleted the battery was, how many times it's been discharged below 10.5 Volts, issues with acid stratification, age of the battery, etc.

A relatively new battery that's been discharged below 10.5 Volts may show no signs at all that it's been damaged. It may start the car and hold a charge with no issues at all. But the damage is there nonetheless and will eventually show up in a shorter lifespan down the road.
 
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Chief, I think that there are exceptions to this lead sulfate crystal reversing when a high rate charger is used. For instance, forklifts and golf carts routinely discharge their batteries below 10.5 volts. They use a high charging current to break up the sulfites.

I've seen dead forklift batteries (that wouldn't take a charge) restored by hooking them up to a really high charge rate - such as from a DC engine driven welder.
 
Scsmith42 said:
Chief, I think that there are exceptions to this lead sulfate crystal reversing when a high rate charger is used. For instance, forklifts and golf carts routinely discharge their batteries below 10.5 volts. They use a high charging current to break up the sulfites.

I've seen dead forklift batteries (that wouldn't take a charge) restored by hooking them up to a really high charge rate - such as from a DC engine driven welder.
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Perhaps...but keep in mind that not all lead acid batteries are designed and maintained the same. While the underlying principles are the same, construction and maintenance are not necessarily so.

Submarine batteries are big honkin' lead acid batteries. But they have specific maintenance and charging processes than car batteries. Even so, individual battery cells are monitored throughout their lifespan and sometimes cells are jumpered out for various reasons.

Car batteries are not subject to various different types of charging methods, such as a "normal battery charge" and an "equalizing battery charge" which are conducted on the lead acid batteries on submarines. (Though some modern vehicles do have "smart" charging systems that may deviate from the typical car battery charging system most of us are familiar with.) These types of charges are meant to maintain the battery at peak health throughout its lifetime. They don't "correct" permanent damage so much as they "maximize" battery capacity throughout its life by maintaining what can be charged in as healthy a condition as possible.

I've no experience with forklift battery maintenance and charging, but looking at what I could find online, it appears that it's similar (but not exactly the same) as for submarine lead acid battery care. They require maintaining a battery water level log (most all car batteries are sealed batteries which can't be watered), limitations on the numbers of battery charging cycles per year (a warranty issue), not over charging them (car batteries are continuously charged while the vehicle is operating), maintaining the full charge times during charging (not interrupting them prematurely), the performance of an equalizing charge (which isn't there to reverse sulfate crystalization), etc.
 
So…. lolz

According to the auto zone tester, the battery and alternator are both good…. Checked the battery a bit ago myself and it was 12.4v off, 14.18 running
 
Burt Gummer said:
So…. lolz

According to the auto zone tester, the battery and alternator are both good…. Checked the battery a bit ago myself and it was 12.4v off, 14.18 running
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That's because you went to autozone. They are MORONS

You need to test them independently. Take them off and test them at Napa or O'Reilly
 
LeeMajors said:
That's because you went to autozone. They are MORONS

You need to test them independently. Take them off and test them at Napa or O'Reilly
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I went to two napas here locally and they both said they didn’t do tests on them.
 
Diablos said:
oreillys, they've tested a few batteries/alternators for me
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I’m going there after the monsoon from the hurricane passes first of the week
 
It's not an "AutoZone" thing...it's a "person doesn't understand how to do this" thing.

My SILs battery issue I talked about above? I went to NAPA to get the battery tested and to get the replacement (it had a NAPA battery in it and SIL was fine with going with the same).

I pulled up in front of the NAPA store, left the vehicle running (in case the battery decided it would give me a problem) and had the guy come out. My plan was to shut the vehicle off, let him test the battery, then start it up and have him run the alternator test.

He just hooked up to the battery while the vehicle was running and pronounced the battery "good".

Ummm...no, you can't do the battery test with the vehicle running and charging the battery. So I just said "screw it" to myself, because I was pretty sure it was the battery anyway, and bought a new battery and swapped it out right there. That's when I discovered the old one was 16 years old, as I unbolted the battery clamp that ran over the battery sticker.


Just because your battery hasn't quite hit 3 years doesn't mean it's not bad. New batteries these days are hit or miss it seems. Used to be you could get batteries with 5 year warranties all over the place. Now the new norm is 3 years. You're having battery problems and the alternator is at least putting out voltage in the proper range. Replace the battery and go from there.
 
Scsmith42 said:
Alamance Electrical in Burlington is great. Pull the alternator and take it to them. They can rebuild it if it needs it, or swap it out.
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Good to know if a place that still does stuff like that. We used to have Battleground Starter and Generator here in my little town of Julian. They don’t do anything anymore from what I can see
 
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