Is it the alternator or the battery?

GymB

GymB

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Wife‘s 2015 Jeep Wrangler. Didn’t start yesterday morning. Jump it and it runs fine, drive around, all good. Stop and start once or twice, all good. Park it for the night and today it doesn’t start. Jump it and it runs fine, 20 min to work all good. Headed home 5 hours later, gotta jump it again. Stop at the grocery on the way home to get steaks, gotta jump it again.

No lights on the dash.

It needs a 30k service and a new airbag (recall item) so headed to the dealer soon anyway, but if it’s the battery I’d rather swap it before I take it to the dealer to save a few bucks. Assuming battery, can anyone suggest a brand, I haven’t bought a battery in years.

Thanks all!
 
drive around as described. Unhook the battery at night. Hook it up in the morning to see if it starts. If it starts, it’s not the battery or alternator, if it doesn’t, you have a draw somewhere.
 
Turn your headlights on & watch them for a few minutes. If it's a bad battery, your headlights will start dimming as soon as the surface charge is burned off.
Crank it & disconnect a battery terminal. If your alternator is good, it should keep running on the power from the alternator w/ the battery completely out of the circuit. You may have to touch the battery cables together or you may not.
The battery that I found w/ the most Cold Cranking Amps (CCA) per dollar was at WalMart.
 
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If you have a volt meter- the battery should be 12.5-13V with the key off, with the engine running it should be ~14.5V. If you're not seeing 14.5V with the engine running above idle, the alternator could be failing.
Many batteries are serviceable, put on safety glasses, pop the cover(s) over the six cells and verify the plates are covered, if not add distilled water, charge, and test.
 
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Walkabout Dan said:
They have a meeter that hooks to the battery that will tell you exactly what the problem is. They do this for free.
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Yep. Been there done that. Replaced the alternator anyway because it was bad.
I mean a bunch of teens pushing buttons isn't a diagnosis.

I have commercial accounts at all the parts houses and find my own part numbers because they can't even do that right.
 
Get Off My Lawn said:
If you have a volt meter- the battery should be 12.5-13V with the key off, with the engine running it should be ~14.5V. If you're not seeing 14.5V with the engine running above idle, the alternator could be failing.
Many batteries are serviceable, put on safety glasses, pop the cover(s) over the six cells and verify the plates are covered, if not add distilled water, charge, and test.
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DIY. GOML is absolutely right. Buy an inexpensive volt meter at Harbor Freight or somewhere else. If you have a bulb that stays on under the hood, in the glove box, or in the trunk, the volt meter will help you find the battery drain.
You need to learn electricity anyway.
 
Thanks all. I’ll check voltage in the morning, but I’d expect lots of problems if it was way low when running. If it looks good I’ll drive it for an hour then disco the battery for 5 hours to see what happens, that last test in the Costco parking lot. Gotta remember to take tools to work tomorrow. Battery is sealed. Walmart has a testing machine on a cart next to the batteries, I’ve been known to make free use of it even if they don’t like it; just don’t want to but from Walmart.
 
ronn47 said:
If it still has the original battery, I'd replace it, it's 6 years old.
Spend the money to get one with as many cranking amps as you can find.
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this.

batteries last on average 3-5 years. i’ve seen them last 6 months and had a guy bring one in that was 11 years old and finally wouldn’t hold a charge anymore.

can’t speak for any other auto parts store, but at advance they range from $120 (1 year warranty) up to $220 (3 year and AGM). if you was close by, i’d check it and get you a discount on one.

also a battery can still have decent voltage (over 12v) but crap for cranking amps. actually had one that was showing 12.50ish volts with only 115 CCA

oh and if a battery light isn’t on (for the most part) the alternator is still charging
 
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Based on what you describe, it's the battery. Classic battery pattern.

Now, you jump it and it dies after about 15-20min, then it's the alternator. Had this problem just the other week. Noticed the lights were dimming badly. Late enough for stores to be closed and about 25min from home. Fortunately, I had a battery booster with me. Hooked it up and sat there for about 30 min as the booster charged the battery. Cranked it up, turned off A/C and headed home. The last couple of miles was on my country road and the car started acting crazy with flickering lights and alarms. I turned off the headlights and made it the rest of the way with a 1200 lumen flashlight being held out the window.
 
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You should never expect your alternator to put a full charge on your battery. It's job is really only to maintain the current charge. Wile it can add some juice to it it's not the same as a good full charge. If your battery dies and you jump the car you really need to get it to a real charger to top off the battery.

Using a battery load tester is different then using a multimeter. A multimeter can still be very helpful though. It is possible to see the right voltage on a battery that is on its way out. You can have a battery that is still putting out full voltage but when you load test it the amperage just isn't there. That only goes one way though. If you do an overnight trickle charge on the battery and the next morning it's only at 9 volts then you know its done and it definitely won't be putting out the correct CCA rating.

It sounds like it is probably your battery but I would get both the battery and the alternator tested properly before you go spending money on things. If you don't trust the kids at AutoZone or whatever then have your preferred mechanic do it. It only takes a minute or two.
 
I’d put it on a trickle charger, but as soon as I do it’ll start to rain.
 
I agree with the above posts. Sounds like it is a failing battery as it's a classic pattern for that. I've had alternators fail. Last time I was on I40 on my way home with about 35 miles to go. Seeing the battery light come on under that scenario is rather unsettling. I turned everything I could off and made it home fine. Recharged the battery and had plenty to make it to the repair shop.

Interestingly I noticed a few days before it failed completely that I could hear an abnormal high pitched whine from the ham radio that was in the car. I suspect that a diode was failing and I was hearing the effect of the ripple current.
 
Most alternators have the regulator internal so the alternator is fine but the regulator fails. I replace the brushes on my original alternators when needed. I had only one replacement fail and it was under lifetime warranty.
 
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C-doodle said:
You should never expect your alternator to put a full charge on your battery. It's job is really only to maintain the current charge. Wile it can add some juice to it it's not the same as a good full charge. If your battery dies and you jump the car you really need to get it to a real charger to top off the battery.

Using a battery load tester is different then using a multimeter. A multimeter can still be very helpful though. It is possible to see the right voltage on a battery that is on its way out. You can have a battery that is still putting out full voltage but when you load test it the amperage just isn't there. That only goes one way though. If you do an overnight trickle charge on the battery and the next morning it's only at 9 volts then you know its done and it definitely won't be putting out the correct CCA rating.

It sounds like it is probably your battery but I would get both the battery and the alternator tested properly before you go spending money on things. If you don't trust the kids at AutoZone or whatever then have your preferred mechanic do it. It only takes a minute or two.
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I agree that most batteries don't get fully recharged, especially if the vehicle is primarily used in city. The vehicle simply doesn't stay on long enough to fully charge. I've taken to periodically hooking up the battery to a charger overnight. You can tell the difference.
 
Lots of stuff on batteries.

The average battery is reliably good for about 3 years. After that, you're on borrowed time and should consider yourself blessed for each additional month of reliable service.

If you shell out the bucks for a higher quality brand name battery with a 5 year warranty, then it should be reliable for 5 years, after which you're on borrowed time.

Once you approach those times on your battery, you should be budgeting for a preemptive replacement. DON'T WAIT FOR YOUR BATTERY TO DIE AT THESE AGES.

Why, you ask?

Because a dead battery is horribly heavy load on an alternator, that's why. You risk damaging your alternator and compounding your problems. A damaged alternator, in addition to being an added expense, also means you could damage your brand new battery you just bought.

SO...preemptively replace your old battery AND at the first sign of battery problems get it checked and replace it if necessary right then.

BATTERY DAMAGE:

If you kill your battery (your battery terminal voltage drops below about 10.5 Volts), you've damaged your battery and, contrary to what some people believe, that damage CANNOT be reversed.

Excessive discharge affected the chemistry of the battery, causing sulfate crystals to form, and once formed these crystals are permanent. No amount of charging will reverse this.

Now, if your battery was in otherwise good health, this may only mean a small reduction in battery capacity that you may not notice...but the damage is there, nonetheless.

If you're at, or past, your service life for your battery and this happens...budget and replace it.

REPEATED JUMPING also runs the risk of damaging your battery/alternator as well. At the very least, you're not paying attention to what you're car is telling you by continuing to live with a problem. If your jumping a lot, go to a parts store, have them check your battery/alternator (it's free), and replace as required.

ELECTRONICS...

Modern cars may be more finicky on battery voltage than cars of years gone by. This is due to their electronics. In past years there were several things people used to do/check to see if they had a battery problem or not. Like check starter operation with the headlights on, for example. In a newer car, you may find that while a battery SEEMS strong enough because the engine cranks well, the battery may not actually be strong enough to power the on board electronics with the proper voltage at the same time.
 
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RetiredUSNChief said:
Lots of stuff on batteries.

The average battery is reliably good for about 3 years. After that, you're on borrowed time and should consider yourself blessed for each additional month of reliable service.

If you shell out the bucks for a higher quality brand name battery with a 5 year warranty, then it should be reliable for 5 years, after which you're on borrowed time.

Once you approach those times on your battery, you should be budgeting for a preemptive replacement. DON'T WAIT FOR YOUR BATTERY TO DIE AT THESE AGES.

Why, you ask?

Because a dead battery is horribly heavy load on an alternator, that's why. You risk damaging your alternator and compounding your problems. A damaged alternator, in addition to being an added expense, also means you could damage your brand new battery you just bought.

SO...preemptively replace your old battery AND at the first sign of battery problems get it checked and replace it if necessary right then.

BATTERY DAMAGE:

If you kill your battery (your battery terminal voltage drops below about 10.5 Volts), you've damaged your battery and, contrary to what some people believe, that damage CANNOT be reversed.

Excessive discharge affected the chemistry of the battery, causing sulfate crystals to form, and once formed these crystals are permanent. No amount of charging will reverse this.

Now, of your battery was in otherwise good health, this may only mean a small reduction in battery capacity that you may not notice...but the damage is there, nonetheless.

If you're at, or past, your service life for your battery and this happens...budget and replace it.

REPEATED JUMPING also runs the risk of damaging your battery/alternator as well. At the very least, you're not paying attention to what you're car is telling you by continuing to live with a problem. If your jumping a lot, go to a parts store, have them check your battery/alternator (it's free), and replace as required.

ELECTRONICS...

Modern cars may be more finicky on battery voltage than cars of years gone by. This is due to their electronics. In past years there were several things people used to do/check to see if they had a battery problem or not. Like check starter operation with the headlights on, for example. In a newer car, you may find that while a battery SEEMS strong enough because the engine cranks well, the battery may not actually be strong enough to power the on board electronics with the proper voltage at the same time.
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my father was a mechanic and he believed in everything you shared. I’ll add one thing I learned from a manufacturer. I sold stainless steel and one of my customers was a Battery Plant. One of the engineers told me that there was no difference in a 1 year Battery and a 4 year Battery. The difference you pay in the store is for the warranty. Also most Battery warranties are pro rated, so your replacement varies on how old it is. Not sure if it’s still offered, but I bought a battery from AAA when mine died while traveling. It came with a 3 year full replacement warranty. Even though I was sort of at their mercy, far away from a parts house, I found out the price was very competitive with what you would pay at Advance or Auto Zone. At about 2 1/2 years old, it went bad and they came out replaced it free labor too.
 
Etruett said:
my father was a mechanic and he believed in everything you shared. I’ll add one thing I learned from a manufacturer. I sold stainless steel and one of my customers was a Battery Plant. One of the engineers told me that there was no difference in a 1 year Battery and a 4 year Battery. The difference you pay in the store is for the warranty. Also most Battery warranties are pro rated, so your replacement varies on how old it is. Not sure if it’s still offered, but I bought a battery from AAA when mine died while traveling. It came with a 3 year full replacement warranty. Even though I was sort of at their mercy, far away from a parts house, I found out the price was very competitive with what you would pay at Advance or Auto Zone. At about 2 1/2 years old, it went bad and they came out replaced it free labor too.
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That's the same as Costco. Iirc it's a 42 month full replacement. It was 42 months, I exchanged 2 from my f350 in January but I don't recall if it's 42 now or 36. But it's still a full replacement
 
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