Author Topic: Low voltage on a new(ish) battery  (Read 483 times)

Offline King of the Hill

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Re: Low voltage on a new(ish) battery
« Reply #25 on: January 17, 2018, 05:33:12 PM »
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.

I've done this a zillion times on older vehicles,  When did the computer start killing the motor when you pull the battery cable?
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Online MassJK

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Re: Low voltage on a new(ish) battery
« Reply #26 on: January 17, 2018, 06:01:39 PM »
you dont have a battery problem you have a charging problem
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Re: Low voltage on a new(ish) battery
« Reply #27 on: January 17, 2018, 06:04:25 PM »
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.

I've done this a zillion times on older vehicles,  When did the computer start killing the motor when you pull the battery cable?
xj alternator is regulated by the ecm if the ecm doesn't see good voltage it  starts doing weird stuff. it will tell you long before the battery is dead
Quote from: Mrs. Whoopie Pies
Then we have those guys that feel like constant cornmeal in ones pants . Alan for example.

Offline bigdaddymack51

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Re: Low voltage on a new(ish) battery
« Reply #28 on: January 18, 2018, 07:27:53 AM »
Deep Cycle batts can handle 10 amp charge. Normal crank batts should be 2/10 amps. This sounds like an alt. issue to me.  A normal standing batt will show 12.6 or better. A standing batt showing 12.2 or less has either a bad cell or not being charged. A load test will tell you if its a batt condition or an alt issue. Not really good to load test a depleted batt.   A simple test is to use a multimeter  while running and one by one turn on all acc. It should be able to keep up staying in the 13/14 volt range. The voltage regulator is inside the alt and senses load and makes adjustments as needed. A simple loose ground wire will deplete a batt .   FjR68

Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #29 on: January 18, 2018, 07:47:36 AM »
So I let the battery charge for a few hours last night at 10 amps, switched it over to 2 amps and let it charge over night. The green light on the charger was on this morning indicating it was fully charged. Since the battery took a charge I think it's safe to rule out a dead cell or something like that. I checked the battery cables and everything was good and tight and in good condition. All the cables under the hood are 2 AWG with heavy copper connectors and only a year old. I'll look at the alternator tonight, and also maybe try swapping in a different computer since the voltage regulator is in the computer on these Jeeps. I didn't want to try and do any more charging system tests last night because I wanted to let the battery charge. Don't need to ruin that for no reason.
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Offline YJScrounge

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Re: Low voltage on a new(ish) battery
« Reply #30 on: January 18, 2018, 08:11:04 AM »
The battery may have come up to charge but can it hold it? Load test the battery.

I had a simular thing happen with my YJ two years ago. Battery tender to full charge, put it back in, used it a couple days. Died at the McDonalds on the way to our first cut at Bobwrika.

New battery, no issues since. I think Alan is on to something with the heat sensor. Another way to test this is put a different battery in it and see if your problems change.
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Re: Low voltage on a new(ish) battery
« Reply #31 on: January 18, 2018, 08:34:16 AM »
He had the battery tested it's fine other than low charge which makes sense if his jeep isn't charging and he was driving on it
Quote from: Mrs. Whoopie Pies
Then we have those guys that feel like constant cornmeal in ones pants . Alan for example.

Offline SJJEEP

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Re: Low voltage on a new(ish) battery
« Reply #32 on: January 18, 2018, 08:42:20 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

I would double check the ground like Alan said

Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #33 on: January 18, 2018, 09:00:36 AM »
I think Alan is on to something with the heat sensor.

Checked the sensor with an Ohm meter yesterday and it was within spec. If I can find my spare sensor I'll swap it out before I put the battery back to be sure.


I would double check the ground like Alan said

Checked the battery cables yesterday and didn't find any loose. Forgot to check the ground going to the block though so I'll check that when I get home today. Nothing I checked was even remotely loose though.
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Offline A new level

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Re: Low voltage on a new(ish) battery
« Reply #34 on: January 18, 2018, 10:45:43 AM »
I’m surprised you don’t have 10 alternators kicking around hahaha
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Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #35 on: January 18, 2018, 12:14:34 PM »
I have two of them but neither one feels very good. Been looking for an excuse to upgrade the alternator before I hooked the winch up anyway. I have another computer I'll throw in after work and try that, if it has the same issues and everything else is checked, I'll pick up the Dakota alternator I was wanting to get anyway.
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Re: Low voltage on a new(ish) battery
« Reply #36 on: January 18, 2018, 12:22:02 PM »
Is the Dakota internally regulated
Quote from: Mrs. Whoopie Pies
Then we have those guys that feel like constant cornmeal in ones pants . Alan for example.

Offline RedJeepster1

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Re: Low voltage on a new(ish) battery
« Reply #37 on: January 18, 2018, 12:30:06 PM »
Is the Dakota internally regulated

Can't find the info at the moment, I'll look to confirm, but 99% sure it is externally regulated like the current one, and if you get a 2000-2003 it will even be the same exact plug as my 2000. You have the clearance the bracket slightly to fit the higher capacity alternator, but otherwise it is bolt in.

Edit: I know someone running this setup, I just sent them a message to see if there was anything else they had to change.
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Offline JeepinMaxx

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Re: Low voltage on a new(ish) battery
« Reply #38 on: January 18, 2018, 07:18:39 PM »
I ran a 1998 Dakota Alternator on my YJ's 1992 4.0L.  It's pretty high output and when I would put a big load on it (winching) the belt would jump a rib (I kept the stock Dakota pulley which is one rib wider than Jeep.  Also fried my fusible link.  So I went back to stock.  If you already upgraded your cables - you should be fine
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