What exactly happens when a battery dies? And is mine "dead"?

[NiceGuyEddie]

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Story:

I have an 18-year-old Optima battery. The car has always sat in the garage for the hot months about June-November. I'd take the cover off and start it up mid-summer. Never a problem.

Until a year ago, I never owned a battery tender. I bought one day after the car had trouble starting. After 48 hours of charging, no issues.

Until recently - a few weeks ago I took a drive for some glamour shots. I stopped the car every 5-10 minutes about 12 times. The starter had a harder and harder time turning the engine over, this never happened.

Anyway, on the drive for the photos, I was surprised the volt meter read 10V with the car running. It was always, always a tick under 15V. I headed home at night and in about an hour the meter read 10V, 9V, 8V, maybe 7V by the time I got home.

After 48 hours on the trickle charger, the battery read 12.8V on a multimeter. The car started perfectly. A multimeter read 14.8V on the alternator and battery when running. The dash Volt meter as before read a tick under 15V.

So I've been driving the car recently and everything is as it has been for the past 18 years. No trouble with starts, and I have not been hooking up the tender when I get home. The gauge still reads a tick under 15V.

The dumb questions are:

What could have happened the day the voltage kept dropping?

How does one know a battery is 100% kaput?

If you go to Autozone and they hook up that battery tester, how exactly do they know the battery is bad?

[Windsor]

Most of the battery testers at the auto parts stores put the battery under a mild load and measure the voltage drop.

Sounds to me like your alternator is kaput.

[flyboyjy]

It's called a load test. It puts a load on the battery and is able to measure the CCA left and usually a % of battery life left. A good battery tester will also recommend, charge and retest, call it a good battery or call it a bad battery and to replace it. Any auto parts store worth going into should have a battery tester that can do all this.

[David Williamson]

Battery that old is on at best borrowed time. But odd the voltage dropped one time like the alternator was not charging and then the next time it was OK. Maybe a loose wire or ground is bad?? I think it's worth getting a new battery and check all the wiring
David W

[rich grsc]

When a battery is dead, nothing happens. No start, no lights no nothing.

[NiceGuyEddie]

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If only I wish how I wired my Voltage gauge. I'd like to check a few more things - does the Volt meter measure the Voltage of the system, or just the voltage of the battery?

I did notice that with the engine running, the Voltage on the alternator was the same as the battery terminals, about 14.8V jumping around a bit.

My headlights also dim a little when at idle, and the fan slows a bit. We've learned that this is due to my underdrive pulleys, but why doesn't the volt meter move at all when I rev the engine? If the headlights are dim, I would think it's temporarily at 10V or 11V at idle, then the needle moves around when revving the engine.

[MB750]

If your voltage meter said 10 VDC after running around town, that's an alternator issue.

Alternators rectify the AC voltage to DC voltage, and the regulate it to something in the 14 VDC range during normal RPMs. That's what charges your battery. Fire up your car, disconnect the battery and test the voltage at the battery leads. That's what the alternator is putting out. My guess it's low based on what you just said above.

If you check your volt meter after you've charged your battery externally, of course it'll say 14 VDC. It'll slowly drop as your car's loads lower it (and make the starter labor more)

[DanQ]

The voltage dropping while motor running indicates an alternator failing. Sometimes they stop charging, then begin again, but it is on its last leg, so it would be wise to replace it now. An 18 year old battery is also begging to fail you at the worst time, so it, too should be replaced. They don't last forever, so why not change them both at your convenience, not when they finally die. You got your life out of them, let them go to auto parts heaven.

[F500guy]

Your drawing is an ammeter, not a volt meter, very different measurement. According to the drawing, the battery is charged thru the meter, that is why it has 10 gauge or larger wire. Technically, the battery positive terminal would be slightly lower than the alternator output due to voltage drop in the system, but not by much. 18 year old battery, wow that's a good run! Battery has individual cells in that will start to sulfate build up and short out across individual cells, thus lowering the ability for the battery to stay at 13+ volts. each cell is worth 2.2 volts. 6 cells in a 12 volt lead acid battery. Then you lose the power available for the battery and it fails a load test.

[tonywy]

What happened to me one time, I got on it, corrected the rear, my elbow hit the battery cut off and I didn't realize it. I noticed the weird battery voltage but didn't know it until I was home.

[jab351w]

Do you have a Ford 2G alternator? If so, check (i.e. remove and inspect) the harness connector for overheating. Or better yet replace it with a 3G before it catches fire. See:

https://www.garysgaragemahal.com/96-...or-repair.html
https://www.crownvic.net/ubbthreads/...&Number=617089
https://www.fullsizebronco.com/threa...issues.499326/

[ggunter]

Wow you got your monies worth out of that one. As batteries sit for long periods of time the lead plates in the battery start to shed tiny amounts of lead. When these tiny amounts of lead build up in the bottom of the battery case, they will cause a short across the plates and give you a shorted cell. When the cell shorts it tries to keep itself "charged" by the rest of the voltage in the other non- shorted cells until the battery dies and no amount of charging will bring it back up. All new charging voltage goes directly into the shorted cell. Ever had a car that would not start with a hot shot? It's because of the shorted cell taking all the incoming voltage. Starting an engine from time to time really takes more out of the battery then puts back in unless you run it for approx. a half hour. Keeping a battery on a tender greatly reduces the amount of lead shedding and extends the battery life. 17 years on a battery is phenomenal.

[NiceGuyEddie]

OK this is getting just too weird. I'm gonna have to shut up and buy a new battery - I was hoping to understand what happened first.

Last night I started up the car and for the first time in my life - or at least the first time I ever noticed, the Volt meter indeed moved when revving the engine at idle.

With the key ON it read about 12.5V. Then after startup the needle would move with rpm. This happened for about 3 minutes, then I went out for a drive and it stayed steady at about 14.5V regardless of RPM or any accessories being used. I put on all of them - headlights, footbox blowers, heater, fan, - I even put on the wipers and hazards.

The only thing I can think of is the battery dropped to a point where it would not take a charge from the alternator, but it would accept a trickle charge on a tender over a period of 48 hours.

Now I have to read all those recent threads about how Optima batteries suck nowadays...

[MB750]

Now I'm pretty sure it's aliens.

[BornWestUSA]

OK this is getting just too weird. I'm gonna have to shut up and buy a new battery - I was hoping to understand what happened first.

Last night I started up the car and for the first time in my life - or at least the first time I ever noticed, the Volt meter indeed moved when revving the engine at idle.

With the key ON it read about 12.5V. Then after startup the needle would move with rpm. This happened for about 3 minutes, then I went out for a drive and it stayed steady at about 14.5V regardless of RPM or any accessories being used. I put on all of them - headlights, footbox blowers, heater, fan, - I even put on the wipers and hazards.

The only thing I can think of is the battery dropped to a point where it would not take a charge from the alternator, but it would accept a trickle charge on a tender over a period of 48 hours.

Now I have to read all those recent threads about how Optima batteries suck nowadays...

The alternator needs 12 volts to begin charging, your battery dropped too low to "excite" the alternator.

Cars with electronic ignition/injection I've seen low battery voltage prevent ignition/injection while it cranks below 9.6 battery volts also.

Old school generators would start charging even with a dead battery from engine RPM alone, think push starting a car or hand propping an old airplane.

But getting over 8 years out of an optima was a good ROI! Time to get a new one!!

[kgkeys]

Alternators can also go bad in such a way that they put out 14-15V but just don't produce enough current to do any good. You have a coil that goes open or short or whatever, and it'll still show voltage, but it can't charge the battery.

Kyle

[Nigel Allen]

The alternator needs 12 volts to begin charging, your battery dropped too low to "excite" the alternator.

Cars with electronic ignition/injection I've seen low battery voltage prevent ignition/injection while it cranks below 9.6 battery volts also.

Old school generators would start charging even with a dead battery from engine RPM alone, think push starting a car or hand propping an old airplane.

But getting over 8 years out of an optima was a good ROI! Time to get a new one!!

Old cars and planes run Magneto's, which operates independently of a battery.

[NiceGuyEddie]

I've been driving the car as much as possible and the battery has been perfectly fine with short trips and 1-2 starts in between. The tender light goes back to green after about 1 hour plugged in.

I can probably make it to the end of the driving season, which for me is early June. After that, time for a new battery. I understand batteries don't like the heat, and it's over 100º in my garage almost every day late June-October.

[rich grsc]

battery don't like cold

[svassh]

It does seem strange and like the behavior of batteries has changed. I grew up in WI cold weather and can remember being able to tell when a battery was dying by the speed at which it turned the engine during cranking. Fast forward 30 years in Texas and with the heat the battery is fine one day next day dead and will not charge or even crank the engine.

[Alan_C]

Eddie, getting that kind of life out of your battery is amazing. As said, even if it is not the core issue, it is on borrowed time. Take the battery and the alternator to a local auto parts store that can test them, then replace what is indicated as being bad.
As said, batteries when completely dead won't do anything. The won't charge or hold voltage and cannot be jumped. More typically, one cell in the battery will fail resulting in lower voltage at full charge and fewer cranking amps. Now that I have been living in AZ at 5000 ft. for almost 7 years, I can say that the winters are really hard on the batteries with all the subzero temps we have seen. I was spoiled on the battery life we saw in CA as I am seeing more like 4 years on the cars that sit outside.

[Mastertech5]

If your battery has a dead cell it will read about 10.5 volts with the engine not running. Each time a battery dies completely it loses its ability to maintain a charge as fully as before and hold it. A draw of more than about 25 milliamps with everything off is too much. This <25 milliamps draw is from keep alive memory, clock, computer, radio and such. A bad diode in the alternator can also be a problem.

[BradCraig]

Wow. You won't get that life out of a new Optima!

[NiceGuyEddie]

6-MONTH UPDATE

I've had the trickle charger on the battery all the time now, even if leaving the car alone for a week. The 18-1/2 year-old Optima battery has worked perfectly since then. Probably maximum 12 starts per outing but still, it works perfectly.

Looks like the keeping the trickle charger on all the time is the key.

The charger is a NOCO Genius 1, cost me $39.99 I believe, currently selling for $29.99

[Alan_C]

Eddie: You may have the record for battery life on your Optima. With the Odyssey I used in my MK4, I always kept the car on a trickle charger, Battery Tender in my case. I never had an issue in the four years I had on the battery and the 2nd owner kept the Odyssey for another 4 before buying an Optima. My guess is the newer Optima did not have the service life of the Odyssey or older Optimas.
Sir you have more than obtained your moneys worth on that one.

[michael everson]

I would buy a new battery but dont get rid of the old one. Keep using it until it dies. Who knows how long it will last. would be neat to see just how long it goes. I once got 12 years out of a GM battery in my Corvette.
Mike

[mikeinatlanta]

While your battery is old and no doubt lived past a normal life, the symptoms you describe are failing alternator. Any changes you are seeing surrounding your recent charging methods are coincidental. If you want to measure your battery power put a proper ammeter and volt meter on it, then measure actual output and voltage drop during start.

All batteries degrade with time and yours is no exception. The potential harm of a weak and old battery, even if it will start your car, is twofold. 1. When your alternator does finally go completely bad you will have a much shorter time between initial voltage drop and being stranded. 2. The reduced amp capacity results in greater voltage drop during start. This voltage drop causes pitting of the starter armature, which will reduce starter power and life.

You really should replace the battery and start shopping an alternator.

[CraigS]

I have no idea how these modern battery testors work but I am convinced the good ones are magic. 16-18 years ago I worked as a Lexus tech and we had the old style SnapOn battery tester. It put an actual load on the battery to test it. Then Lexus sent out a new all electronic high end testor. A couple weeks later I did a service on a car and was asked to test the battery. Lexus testor said it's health was bad. (Yep tester printed out a small slip rating the battery right now and for the future-it's health) Old testor said it was OK. The owner was cool and decided to keep his battery. 5 weeks later the service advisor said hey remember that guy we tested his battery w/ both testers? Yeah. He just called and told me we should trust that new tester. He was on a trip and came out of hotel one morning and battery was dead. I retired 10 yrs ago so don't have access to a Lexus tester any more. I replace our batteries at 5 years. It is just not worth it to me to have a dead battery since they never ever die in my driveway. Especially I don't want my wife to have a dead battery by herself.

[J R Jones]

I have had a motorcycle battery (Yamaha tour bike, not a shaker) go bad at a gas stop on a cross country trip. Internal short methinks.
This year my RV batteries (two coach, one engine) tested good out of seasonal storage and maintenance charging. Kind of easy duty in an RV.
Two weeks ago the coach batteries were at 10.6 volts. I tried charging them in parallel and individually and my higher end charger said the voltage was 13-14 but they would not go to 100% charge.
Left overnight un-attached, they drop to 9.6 and 10.6. They died as a couple, and the charger knew it. Redundant systems are convenient.
jim

[Jeff Kleiner]

I would buy a new battery but dont get rid of the old one. Keep using it until it dies. Who knows how long it will last. would be neat to see just how long it goes. I once got 12 years out of a GM battery in my Corvette.
Mike

I have that one beat Mike! Bought a 2003 Dodge Ram pickup in October of '02 and sold it in March of 2016 with the same battery still starting it every day. Over 13 years---unbelievable. Other side of the coin the battery in my 2020 Ram pickup died after a little over 2 years. Obviously they've changed suppliers!

Jeff

[Railroad]

I bought a Duracell from batteries plus, lasted the warranty and had it checked. They told me, dead cell. I thought that was just too easy and went to Sam's and had it checked. He put the tester on it and immediately from his mouth came, dead cell.
How can they cast in a weak link that last exactly the warranty time of the battery?

[NiceGuyEddie]

I took some measurements today:


Battery: 12.1V across terminals

Alternator: 15.5V if >1,000 rpm

Alternator: 13.5V if <1,000 rpm (when idling) But sadly, the headlights still dim at the stoplight. But it's already proven that the problem is caused by under-drive pulleys. I do wonder why they are so dim if it's running at 13.5V.


Oddly, the meter on the dash always shows 18V when running. It does not move when the car is at idle. And it does not move when revving the engine. It should, of course.

The only time the meter on the dash was NOT at 18V was back when I was racing home because the battery is dying.

The battery is in the trunk keeping cool, that may be part of its long life.


EDIT: I'm not smart enough to have taken a reading across the battery terminals with the tender plugged in. It will probably read the same 12.1V but it would be an interesting data point.

[lance corsi]

Sounds like a poor ground connection.

[Avalanche325]

I am pretty sure the gauges are dampened, so they don't jump around. So you won't see much on a rev.

If you are running a one wire alternator, they can stop charging at low RPM. If you are running a real alternator :-), it sounds like you may be due for a new one.

Of course, check and clean your connections first.

[J R Jones]

I took some measurements today:


Battery: 12.1V across terminals

Alternator: 15.5V if >1,000 rpm

Alternator: 13.5V if <1,000 rpm (when idling) But sadly, the headlights still dim at the stoplight. But it's already proven that the problem is caused by under-drive pulleys. I do wonder why they are so dim if it's running at 13.5V.


Oddly, the meter on the dash always shows 18V when running. It does not move when the car is at idle. And it does not move when revving the engine. It should, of course.

The only time the meter on the dash was NOT at 18V was back when I was racing home because the battery is dying.

The battery is in the trunk keeping cool, that may be part of its long life.


EDIT: I'm not smart enough to have taken a reading across the battery terminals with the tender plugged in. It will probably read the same 12.1V but it would be an interesting data point.

Ed,
This thread is obscured by addressing two issues: Your very old battery, and your headlight dimming at idle.
If you question your battery, have you swapped it out for a new battery and checked your indications, including headlights at idle?

* When you measure 13.5 volts at idle do you measure at the battery or at the headlight?
* If the headlight is dim at 13.5 volts, how is the brightness attached to a new 12v battery?

If the idle voltage at the headlight is low, but measures 13.5v at the battery, you have harness and switches to troubleshoot.
BTW there is voltage drop from the trunk to the front of the car, especially with smaller wire gage.
jim

[NiceGuyEddie]

UPDATE:

It's been over a year since my car was running under-Voltage and I was considering replacing my (then) 18-year-old Optima Battery.

The update is since then, I have always, always, always, plugged in the battery tender after I got home. (I heard it's best to wait an hour for the battery to cool down. Might be a myth, though.)

Since then, I have had a few hundred starts, re-starts, and no running Voltage issues.

Lesson learned: If you have a good, modern, trickle charger, use it always!

Very impressed with this Optima (RED) battery. I still have the original receipt from when I was building!

[CraigS]

Not sure about that Eddie. If your battery won't stay charged for at least a week, either the car is draining it or it is toast. Over theyears I have had too many experiences w/ batteries that suddenly die. Not my own but, friends and customers. I spent 20 yrs as a Lexus tech. One story I will never forget. from 20 yrs ago now. Had a customer come in, get a service and ask that his battery be checked as he was leaving on a trip. We had been using a SnapOn carbon pile tester for ages but several months ago had gotten a new electronic tester from Lexus. The new tester said it had a marginal life expectency. Service advisor asked me to use the old tester. It said battery OK. So owner headed out. Battery lasted for his trip but 2 months later he called the service advisor. Just an FYI, trust that new testor because my battery just died. Now that I am retired I don't have a highend tester to use so I replace all our personal batteries every 5 years. It is just not worth it to me to tempt fate leaving my wife w/ a dead car at 9pm at the mall or wherever.

[BornWestUSA]

A battery that is 12.1 volts at rest is bad. I would replace the battery under 12.3 volts for peace of mind.

Normally such measurements are taken after the "surface charge" is removed with a light load, like turning on the headlights for a few minutes.

Or the day after normal driving.

Also when charging if it goes over 15 volts that is another indication of a "bad" battery.

Mind you this is all based on regular "old" tech 12v lead acid batteries, your optima may skew things a bit?