Jeep battery or alternator dead?

I'm pretty good under the hood, but this has me stumped. Intermittently, when I start the 99 Wrangler (4.0) it acts like the battery is almost dead. I hook up the handy dandy battery tester (engine off) and it shows full charge. I start the engine and the tester says alternator is charging at 100%.

I put in a Napa remanufactured alternator last summer and the battery is 2 years old. WTF is going on here? What's wierd is that it's intermittent.

ETA: I already cleaned the battery terminals and the connections to the alternator look clean.

I don't know what tester you're using, but do you have access to a digital multimeter?
I prefer real voltage readings over an good/no good light

It could also be a dead/shorted cell in the battery- would show those symptoms... have the battery load tested... unlikely at 2years, but you never know.

Check grounds?

Wait, when you say act like the battery is almost dead, do you mean a slow turn over? Could it be the starter is getting tired?

How many amps is the starter pulling?

I think I have a multimeter around here somewhere. I'm not real good with electrical stuff so I've used it very rarely. I forgot to mention that I did the battery down to nothing a few weeks ago - left a compressor plugged in to the cig lighter and the ingnition on all night.

I've seen similar problems from a corroded battery cable, connector, or battery terminal.

Pull both cables off, give them a very good cleaning, rough up the battery terminals, and re-tighten.

I had one battery cable, looked ok, but a twist of the connector at the end of the cable and the wire just disintegrated, it was completely corroded inside. Turns out the battery terminal had been cracked, and was leaking a tiny bit of battery acid right at the terminal for a while.

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Originally Posted by Irving

Check grounds?

Wait, when you say act like the battery is almost dead, do you mean a slow turn over? Could it be the starter is getting tired?

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This is possible I guess. 193k on the odometer on the original starter. I never had a starter go bad like this before though.

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Originally Posted by Graves

How many amps is the starter pulling?

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No clue. I'm pretty ignant on electrical stuff to be honest.

Should be able to get a full ESC (electrical test) for a small(ish) or perhaps free at a local shop. What kind of tester are you using to check the battery? Deep cycling the battery is no bueno.

I'd start with a load test on the battery (free from places that want to sell you a battery, and if you killed it flat, that's possible.. and easier than testing the starter)
Did you put a battery charger on it after you killed it flat?
Is it maintenance free, or what's the water levels?

It could be a bad connection at the starter, or a failing starter, but I'd start looking at the battery since it's easier.

Here's a quick couple of tests to check the alenator, while running, see if a wrech will stick to the back of the altenator. If not weak altenator. Then Start the jeep, pull the positive battery cable, then start turning on the electrical items..... Headlights, radio etc.... Until everything is on or the jeep dies. If the jeep dies, bad alternator.

Clean the battery cable connections.

How old is the starter? The bushings could be going bad and, when hot, can sound like the battery is going dead.

Skip NAPA and go to Vannata's Auto Electric. He does good rebuilds.

Address: 1981 8th St, Boulder, CO 80302
Phone:(303) 443-5775

I'll be around the house all evening if you need a and.

This happens on/off and usually when cold. I'm gonna try some of SideshowBobs tests now. Thanks Tom.

Wrench stuck to the alternator (not super tight, but there was obvious magnetism) and the Heep ran fine for 15 mins with everything on and the + battery cable off. Bad battery looks like. I got the charger on it for tonight just to be safe so I can get to work tomorrow.

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Originally Posted by SideShow Bob

Here's a quick couple of tests to check the alenator, while running, see if a wrech will stick to the back of the altenator. If not weak altenator. Then Start the jeep, pull the positive battery cable, then start turning on the electrical items..... Headlights, radio etc.... Until everything is on or the jeep dies. If the jeep dies, bad alternator.

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With modern electronics, this is a bad idea... worked fine on older vehicles, but especially if there's a problem with your charging system (shorted diodes, etc), then you could fry the computer, etc... the battery acts like a giant capacitor, absorbing voltage spikes, and limiting the overall voltage. Without it in the system (even a bad battery), you could have voltage spikes that destroy electronics.

don't believe me? then ask this guy: http://www.w8ji.com/battery_and_charging_system.htm

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Originally Posted by GilpinGuy

Wrench stuck to the alternator (not super tight, but there was obvious magnetism) and the Heep ran fine for 15 mins with everything on and the + battery cable off. Bad battery looks like. I got the charger on it for tonight just to be safe so I can get to work tomorrow.

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I love the backyard methods, but they're subjective... and there are a lot of variables, if the battery isn't taking a charge, and there's not a large load on the alternator, then it won't stick well... There's nothing like the solid # you get from a Digital Multimeter... check the voltage at the battery right after starting, should be around 14.3-14.4V.. if higher, it will boil out the water, if lower, there's something wrong somewhere
so then you check the Alternator output with the DMM (Digital MultiMeter) ground on the alternator case. If you have around 14.4V there, then the problem is in wiring somewhere... check vs chassis ground somewhere and if that's lower, then you've got a bad ground somewhere- if it's the same, then the problem is in the + feed to the battery.

You have to think of all electrical circuits as a loop- the - has to get to the + eventually, weakest link will prevent it from working.

All that said, I'd put money on the battery still.

A lot of good advice. Diagnostics require more than indicator lights. Typically a fuctioning system will have ~13.8-14.4ish volts at the battery. There are a few obvious things mentioned (battery, alternator, starter). One thing to check is if the voltage regulator is integrated with the alternator. If not, and voltage is out of whack, look for the regulator.

That being said, I've had a brand new battery be completely dead, so it's a possibility.

Modern auto electronics do not like to hit zero volts. A BMW for example requires a system reboot by an authorized dealer, typically an $800 bill.

If that fails, try googling the issue, if you have this, there are probably a few hundred thousand other Jeep owners who have posted their experiences.

Also, if it is the battery, don't skimp, buy an Optima from Amazon Prime.

Turn on the motor and let it run. Take the negative off the battery, if it stays running, the alternator is working. If it dies then bad alternator.

Are Optimas as good as they used to be?

I know someone who works for interstate batteries who has intimated that optima's quality has suffered in the last few years.

I have had good luck with them in the past though.


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Originally Posted by Irving

Are Optimas as good as they used to be?

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I would not put a current model Optima in my vehicle. They used to be good but quality has suffered. Bought one in '98 and it lasted 10 years.

I've been happy with Interstate batteries.

running optima yellow tops for years, no issues at all, i have had a red top fail in the past. the red top is no different than a regualr battery, run it dead a few times and it will not take a charge, the yellow tops are a deep cycle, not affected by running dead.

running in the boat and the trucks,

Optimas are not what they used to be. All the cool off roaders are now using DieHard Platinum batteries.

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Originally Posted by newracer

Optimas are not what they used to be. All the cool off roaders are now using DieHard Platinum batteries.

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Any real basis for this statement?

I've had good experience with Optima, both red and yellow. I wasn't aware of any quality issues. I'll use the Google to check it out.

My second choice for batteries is AC-Delco.

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Originally Posted by bside303

Turn on the motor and let it run. Take the negative off the battery, if it stays running, the alternator is working. If it dies then bad alternator.

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I'll repeat it again:

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Originally Posted by 68Charger

With modern electronics, this is a bad idea... worked fine on older vehicles, but especially if there's a problem with your charging system (shorted diodes, etc), then you could fry the computer, etc... the battery acts like a giant capacitor, absorbing voltage spikes, and limiting the overall voltage. Without it in the system (even a bad battery), you could have voltage spikes that destroy electronics.

don't believe me? then ask this guy: http://www.w8ji.com/battery_and_charging_system.htm

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I provided a source- but I'm an electronics engineer, I should know something about this subject... [gohome]

For the record, I'd do this on my (wait for it... ) '68 Charger
or even my '98 Ram 2500 Cummins (12V)
but no way on my 2007 Charger, or even my '97 Suburban

come on, this is the 21st century... even THIS $5.99 meter would do: http://www.harborfreight.com/7-funct...ter-98025.html
if you're not willing to spend 6 lousy male deer on a meter to really see what's going on, then take it to a shop before you do more damage... and don't give suggestions to people how to ruin their electronics...

For the Record, I'd at least upgrade to the $22 meter at HF- that one is at least a copy of a Fluke meter.

You dont even have to disconnect the battery, if your alternator is bad it won't take long for the voltage to start dropping while running

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Originally Posted by 68Charger

I'll repeat it again:



I provided a source- but I'm an electronics engineer, I should know something about this subject... [gohome]

For the record, I'd do this on my (wait for it... ) '68 Charger
or even my '98 Ram 2500 Cummins (12V)
but no way on my 2007 Charger, or even my '97 Suburban

come on, this is the 21st century... even THIS $5.99 meter would do: http://www.harborfreight.com/7-funct...ter-98025.html
if you're not willing to spend 6 lousy male deer on a meter to really see what's going on, then take it to a shop before you do more damage... and don't give suggestions to people how to ruin their electronics...

For the Record, I'd at least upgrade to the $22 meter at HF- that one is at least a copy of a Fluke meter.

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The old ways are best. [blaster]

HF has $3.00 multi-meters that last fairly well. I just toss it in the tool box or glove box and leave the good one in the shop.

I'm waiting for GG to post up a status before I waste all the time typing three more sentences on what to use the MM for.

Inquiring minds want to know. [2cents]

Quote:

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Originally Posted by 68Charger

I'll repeat it again:



I provided a source- but I'm an electronics engineer, I should know something about this subject... [gohome]

For the record, I'd do this on my (wait for it... ) '68 Charger
or even my '98 Ram 2500 Cummins (12V)
but no way on my 2007 Charger, or even my '97 Suburban

come on, this is the 21st century... even THIS $5.99 meter would do: http://www.harborfreight.com/7-funct...ter-98025.html
if you're not willing to spend 6 lousy male deer on a meter to really see what's going on, then take it to a shop before you do more damage... and don't give suggestions to people how to ruin their electronics...

For the Record, I'd at least upgrade to the $22 meter at HF- that one is at least a copy of a Fluke meter.

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I will agree. Pulling the cable on older cars was easy. Just like pulling the cable and inserting a light to see if something was draining a battery. Now days current is always being drawn. I have a 27FM and an 88 Fluke but also have a few cheap ones. A $9 meter in the camper was better than nothing when ya need it. The one above is what I throw in the car tool kit for trips. Not real accurate but it works.

And a 98 12V 5 speed does not need batteries/alternator as long as the fuel stop solenoid is bypassed. You will not have anything electrical including the dash but it will keep running as long as there is fuel in the tank.[Flower]

I figured I ruined the cheap ass battery I had in there by running it stone cold dead a few weeks ago. I know I've done it once or twice before since I bought it a few years ago. The new battery has been in a few days now - no problems at all.

Thanks for the help guys!