Author Topic: Low voltage on a new(ish) battery  (Read 482 times)

Offline RedJeepster1

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Low voltage on a new(ish) battery
« on: January 17, 2018, 10:34:35 AM »
Found myself having some trouble with my charging system this morning. Volt gauge in the Jeep dropped down to nothing this morning on the way into work. Jeep still ran fine, headlights were just a little dim. It drove with the volt gauge bottomed out for about 20 miles coming into work like this. Never died or hesitated.

Just had it tested at the parts store:
Volts - 12.05
Meassured - 725 CCA
Rated 690 - CCA

Guy at the parts store said dead cell. Battery is less than 2 years old but I got it at cost so no warranty on it. Date sticker is 3/17. Anyone here know anything about battery's and have a second opinion? This was in the XJ, it's a 2000.
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Offline YJScrounge

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Re: Low voltage on a new(ish) battery
« Reply #1 on: January 17, 2018, 10:39:05 AM »
Put it on trikle overnight before hooking it up. Shelf batteries are not full charge. Once you arc them memory is set and will not charge past the point when you installed it. Drinving it doesnt charge it more, just keeps it charged.

I learned this going through motorcycle batteries and installing them not fully charged. Have had great luck with batteries since learning this.
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Re: Low voltage on a new(ish) battery
« Reply #2 on: January 17, 2018, 10:40:19 AM »
12 volts after a dead drive doesn't sound bad.

Check the sensor in the tray. Double check grounds, voltage reg is in the ecm
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Offline King of the Hill

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Re: Low voltage on a new(ish) battery
« Reply #3 on: January 17, 2018, 10:49:26 AM »
12.05volts key off, what was the voltage when running at the battery?  If it was 12.05, it is a charging problem. 

Even if you had a dead cell, with the engine running you would get 13+volts out of the alternator at the battery terminals.

I usually use about 12.6 volts as the standard to meet for a charged battery that has been sitting for a while with no load.
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #4 on: January 17, 2018, 10:56:41 AM »
So just to clarify, this battery has not been sitting for any length of time. It's been in the silver Jeep, which has never gone more than 2 weeks without being started. Battery is out of my Red Jeep and was in that Jeep for maybe a year with no issues. Took the Jeep for a drive last night and I wasn't looking for it, but I don't recall noticing the voltage being low.

I did check the battery this morning at Ian's house when I noticed the issues, and with the Jeep running it was reading about the same, just over 12 volts. It typically reads 13.6-13.8 running and 12.5-12.6 sitting from what I recall.

When I get home today I'll check all the wires. They are all 2 awg and pretty new, built them last summer. What's the sensor in the battery tray? I have seen it but don't know what it does. I have another tray with another sensor in it.
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Re: Low voltage on a new(ish) battery
« Reply #5 on: January 17, 2018, 11:09:32 AM »
It's a temp sensor that tells the ecm how hot or cold the battery is
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Offline Red Rocker

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Re: Low voltage on a new(ish) battery
« Reply #6 on: January 17, 2018, 11:18:16 AM »
If your only measuring 12 volts at the battery while the jeep is running then your charging system is not working, check the clamps and wiring and then the alternator, even if the battery has a bad cell you need to find out why the charging system is not putting out 13+ volts.

The engine is running on battery power only and the voltage will keep dropping to eventually there won't be enough to run the ecm and ignition and the engine will die.

If the wiring looks good and clean and no corrosion then the alternator is most likely bad, it happens.

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Offline MasterDrazhar

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Re: Low voltage on a new(ish) battery
« Reply #7 on: January 17, 2018, 11:27:49 AM »
Start the Jeep, and with it running pull the positive terminal off the batt.

 If the Jeep dies the alternator is shot.

 If it doesn't die, check the voltage, should be somewhere around 14 volts, if it isn't could be the regulator or alternator.
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #8 on: January 17, 2018, 11:28:16 AM »
I’ve got another 35 or so miles on the Jeep since the voltage dropped. If it wasn’t charging at all, it wouldn’t still read 12 volts. That’s why this is confusing. It should have died out completely by now.

I’ll do some more tests when I get out of work. Just confused because it doesn’t seem like a normal dead battery or dead alternator.

Here’s he printout from the Parts store. Done with the vehicle off.




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Offline Red Rocker

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Re: Low voltage on a new(ish) battery
« Reply #9 on: January 17, 2018, 11:38:23 AM »
it's weird that the voltage is low but it's still putting out above it cold cranking amp rating
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Re: Low voltage on a new(ish) battery
« Reply #10 on: January 17, 2018, 11:43:43 AM »
It's most likely  the temp sensor or the ecm.

You can jump the field winding to check alt output.
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #11 on: January 17, 2018, 11:55:25 AM »
So something to note, and Alan maybe this will further support your theory but I didn't think about it before, when I first start the vehicle the voltage gauge reads about 12 volts, it only drops after driving for a minute or two, then drops to 9 and the check gauges light comes on. Wondering if the temp sensor isn't used when the vehicle is first started?

I was reading if it gets a bad signal it will drop the alternator to minimum output though, which would align with being able to drive so far on an almost dead battery without it dying.
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Re: Low voltage on a new(ish) battery
« Reply #12 on: January 17, 2018, 12:04:20 PM »
It's there to stop over charging ( boiling)  the battery. 

The gauge is not an actual reading is an output from the ecm
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #13 on: January 17, 2018, 12:10:29 PM »
Wish I took the multimeter from Ian's I was using to check things this morning. Would have checked a few things on my lunch break.
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Offline Right Wing Curmudgeon!!!

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Re: Low voltage on a new(ish) battery
« Reply #14 on: January 17, 2018, 02:01:51 PM »
If you pull the battery connection while running, it will kill the engine.  It cannot run without a battery.

From the sound of it, you have a charging issue.
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #15 on: January 17, 2018, 02:23:02 PM »
Definitely looks like a charging issue, but question is what and why? Just got home from work, had the parts store do a charging test on the battery since it’s free, results below. I drove the Jeep about 100 miles today and the battery reads 11.36 as it sits in my garage right now, so it was charging at least a little bit. Alternator didn’t completely give up. Gonna go test some other stuff now that I’m home.






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Offline RedJeepster1

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Low voltage on a new(ish) battery
« Reply #16 on: January 17, 2018, 02:59:49 PM »
Ohm tested the sensor and it checks out. Range is 9k-11k at ambient temp, i got 10.8k when I checked it. Checking all my connections now and going to try to track down a charger to see if the battery will take a charge out of the vehicle. I don’t own one, although I probably should.


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Offline JeepinMaxx

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Re: Low voltage on a new(ish) battery
« Reply #17 on: January 17, 2018, 03:21:50 PM »
where are you located?  I have a charger you can borrow for a while
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Re: Low voltage on a new(ish) battery
« Reply #18 on: January 17, 2018, 03:32:29 PM »
with the engine running if you do not see 14 or so volt you need to check the alt and the ecm   there's a way to jump the field to test the alternator.  if you jump the field and get +14 you need to replace the ecm or wire in an external regulator.   dont to leave the field wire jumped out for a long period of time you will kill everything from overcharge
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Offline MasterDrazhar

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Re: Low voltage on a new(ish) battery
« Reply #19 on: January 17, 2018, 03:51:36 PM »
If you pull the battery connection while running, it will kill the engine.  It cannot run without a battery.

 This new?   What brainiac came up with that one...?

   I've always tested alts/batteries that way.

 It's also how we got Catrini's Jeep home from Paragon... swapping batteries back and forth with my Jeep running since his Alt died...

 We would drive till his headlights were dimming too much, then we'd stop and swap batteries with my Jeep running, and my jeep would charge the dead battery while the other ran in his Jeep... Swapped em like that till we got back to Middletown from PA!
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #20 on: January 17, 2018, 03:52:02 PM »
I’ll look into that after the battery charges. So far the little gauge on the charger hasn’t moved. Sitting at just over 50%. My landlord had one in the barn that he said I could borrow so it’s been plugged in since just after my last post. How long would it take to charge. Currently have it on 12V 2A. If it takes a while that’s fine, Jeep can sit for a couple days while I figure out what’s going on.


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Re: Low voltage on a new(ish) battery
« Reply #21 on: January 17, 2018, 04:15:15 PM »
At 2 amp. Like 36 hrs  :rotflmao:
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #22 on: January 17, 2018, 04:20:42 PM »
Haha. Should I set it at 10 amps for an hour or two?


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Re: Low voltage on a new(ish) battery
« Reply #23 on: January 17, 2018, 04:34:19 PM »
10 amp  maybe 4 hrs
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #24 on: January 17, 2018, 05:29:17 PM »
Sorry for the dumb questions. In the last 7 years I’ve owned cars, I’ve actually never had to charge a battery on one of them. I think I mostly didn’t own anything long enough to have a battery problem.


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