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Small battery replaced under warranty and big one?

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So recent get dealer to fix service light for star-and-stop system, and they found small battery defect and replace it under warranty.
But I am worry about the big one is also bad, the car 3 year and 45k km

So basically when I was commute 60km a day, the SNS system always kickin, and since about a year ago I WFH now, I only drive one long trip a week, the system rarely kickin as it always show charge battery, which is NOT BAD at all.
But, until recently service light for SNS is on and dealer fix it by replacing the small battery. Right after dealer work, the SNS can kick-in, as dealer wrote in their job order they charged both battery and found big one was ok and small one is defect.
But a couple of week after, now SNS stop working. During the week I still drive a couple of long 40km trip at least once a week, absolutely not to a point to sit car long to damage battery, so I am worried that big battery is just matter of time to die.

So I put it on battery maintainer overnight, it measured 13.20v with maintainer on, and once unplugged from maintainer for 30min, it drop to 12.48v, and I understand healthy battery should be 12.89v at full charge. Specifically I have two question:
1, is my battery still good given the measurement?
2, how did dealer get it back to a point of charge that SNS kick-in, how long my maintainer can get it back like dealer did.
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I was told by a service mngr at dealer, (while waiting for a fob to be programmed) that both batteries in my jeep should be changed out. They read codes I was throwing. I had bypassed the auxiliary battery and he understood why but also told me when the auxiliary starts to fail it drags on the main and causes damage to it.
Just saying what he said. Also told me they would replace both and provide 3 yr warranty on both batteries for $ 720. 00. I'm tempted to put it back to stock given the warranty. too many computers in these dang vehicles, and one thing effects many others.
That's just my thoughts for what it's worth.
 
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I was told by a service mngr at dealer, (while waiting for a fob to be programmed) that both batteries in my jeep should be changed out. They read codes I was throwing. I had bypassed the auxiliary battery and he understood why but also told me when the auxiliary starts to fail it drags on the main and causes damage to it.
Just saying what he said. Also told me they would replace both and provide 3 yr warranty on both batteries for $ 720. 00. I'm tempted to put it back to stock given the warranty. too many computers in these dang vehicles, and one thing effects many others.
That's just my thoughts for what it's worth.
too many computer things, still the clock slow down 1 min every week, LOL
 
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well, I did more test, I have a fairly smart charger, so I bump the battery to 13.8v, which i figure is the safe top of charge voltage. And the ESS function ready immediately after coolant temperature is up.

So this is the right way to bring your battery back to life, the floater charge I used yesterday will NOT charge battery back to full, but maintain it from FLAT. Question 2 is solved.

After a bit of driving to home, the battery measured 12.57v when stopped, because the battery is still connect to car, so open circuit measure should be little higher, not optimal but better than yesterday, so question 1 the answer is the maybe NOT bad. For comparison purpose, I measured my 2month old jetta, same voltage.

I put 2.57 AH of energy back, typical car battery has less than 30AH useable energy, this is the loss of charge during like maybe 2 week less-driving time.
 

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so question 1 the answer is the maybe NOT bad.
You have a 2018. You already replaced the aux battery. Change the main too. You are near the end of the expected 3 year life span of the OEM battery.
 

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You have a 2018. You already replaced the aux battery. Change the main too. You are near the end of the expected 3 year life span of the OEM battery.
no 2020 JL, about another two year to get off warranty.

So the battery is for 5 year warranty, correct?
 

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no 2020 JL, about another two year to get off warranty.

So the battery is for 5 year warranty, correct?
@modeler

Factory installed batteries = 3 yr. , 36,000 mi. warranty.

Battery(s) need to be load tested in order to know if any good.... if serviceable.

Service Departments are notorious for saying they load tested BOTH batteries but in fact they load tested one or both.... or neither.... 8-(

Take your JL in and ask to please speak to the Service Manager... not the Service Writer...

Speak to the Service Manager and very politely.... again, politely ask to see the paper printout of each of the 2 batteries in regard to their load testing... this way you know both were tested ..... YOU saw the results....

You want to address BOTH batteries if you are close to the end of your 36,000 mi warranty.... and also if you do not want to get stranded thanks to them not doing what they should be doing in regard to testing BOTH batteries..
 

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I'm all for load testing both batteries, but to the novice it may be useful to know what this means.

If a service tech sticks a load tester on the main battery of a dual battery JL they are technically load testing "both" batteries, but in a diagnostically ambiguous way--in other words the test may yield ambiguous results. Don't settle for this.

First, in dual battery JLs the two batteries need to be disconnected, which is as simple as temporarily disconnecting the negative cable from the ESS battery off of the main battery's negative post. Then the main battery can be load tested in isolation by putting the load tester's leads on the main battery's terminals.

Move that negative lead from the load tester over to the dangling cable afterwards and this second test is soley against the ESS battery. Yes---even though the postiive of the load tester is still on the positive teminal of the main battery.

Don't forget to reconnect that negative cable between the two negative posts of the main and ESS battery afterwards.

Those two results yield useful diagnostics about each battery. I am all for load testing done against both batteries independently. Any service tech that tries to sell you that they load tested both batteries in one consolidated test, because the batteries are connected, paradoxically, tested neither.
 
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@modeler

Factory installed batteries = 3 yr. , 36,000 mi. warranty.

Battery(s) need to be load tested in order to know if any good.... if serviceable.

Service Departments are notorious for saying they load tested BOTH batteries but in fact they load tested one or both.... or neither.... 8-(

Take your JL in and ask to please speak to the Service Manager... not the Service Writer...

Speak to the Service Manager and very politely.... again, politely ask to see the paper printout of each of the 2 batteries in regard to their load testing... this way you know both were tested ..... YOU saw the results....

You want to address BOTH batteries if you are close to the end of your 36,000 mi warranty.... and also if you do not want to get stranded thanks to them not doing what they should be doing in regard to testing BOTH batteries..
You find my post funny. There's nothing comedic or wrong about it.

Jeep Wrangler JL Small battery replaced under warranty and big one? 1675184926687


I simply clarified, because you didn't, and believe you should have, that the batteries need to be electrically separated before such load tests can yield useful diagnostic information.

To the novice, be it mechanic or owner, load testing both batteries could mean, wrongly....could even in there minds necessitate (wrongly) that this test be done with both batteries connected, as they are from the factory, when this is a patently wrong diagnostic approach.

Dumb mechanics could equate your sound, but somewhat ambiguous to the novice advice that owners see two printouts with the owner wanting the wrong test done twice.

Let me give you something to laugh about. The word "both" here is a double entendre---the stuff jokes (that are not intended here) are often made of. "Both" could mean to test both batteries independently, which is correct, or to load test the batteries only when "both" are connected, which is wrong.
 

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Dual battery JLs, as many, but by no means all, or maybe even most of you know, are connected at the factory in parallel, and remain so by factory spec barring a few scenarios I'll cover.

I don't cover (or judge) below the various steps owners take to permanently pair, or eliminate one, or replace both batteries.

Parallel connections wire the positive terminals of batteries to each other, and the negative terminals to each other, but those two links between the batteries never electrically touch.

This tends to be done with batteries of similar voltages, and in so doing will create one larger battery whose amp hours is roughly the sum of the individual amp hours of the batteries connected, but whose voltages roughly remain constant despite the pairing.

An appliance that connects to any one of the positive terminals connected together here, and any one of the negative terminals enjoys this longer service life.

(Series connections, the opposite, pair the positive of one battery to the negative of the next, increasing voltage by roughly adding the voltages of the underlying batteries, and roughly holding amp hours constant.)

Each connection methodology has its place in electrical applications, and by no means are they mutually exclusive. DIY solar enthusiasts regularly create large battery banks with both series and parallel connections between the underlying cells towards the goal of reaching a desired voltage and amp hours in ways most efficient to their applications and batteries' chemistries.

The only time your dual battery JL will attempt to separate these 2 parallel connected batteries is for an instant at start, in order to test the ESS battery in isolation, or during ESS events to preserve the main battery to bear the brunt of the load to crank the engine after an ESS event.

(Actually, what happens when an ESS event ends is both batteries are first reconnected, and then both energize the crank, the (ESS preserved) main battery barring most the work here.)

Those two batteries, upon connection won't be at exactly the same voltages, but once connected there will be a tendency for that voltage (provided both batteries are working) to rise somewhat in the battery whose voltage is lower than the other, and vice versa over time. It is this very scientific fact that would find your placing a volt meter on either battery, without disconnecting them, leading you to composite voltage of both batteries, and inconclusive voltage metrics of either battery in isolation. The test might show useful results if both batteries are on their way out, but it might also allow a good battery to cover somewhat for a bad one.

A certain member with the giggles above knows this but forget to mention the importance of isolating the batteries in a voltage test and how. So I did Voltage Check, but because it's important, not because his posts, my posts, or anyone's are always perfect.

Voltage is a simple instantaneous test of a battery which can be thought of like water pressure.

It's a useful diagnostic tool with limitations explained with the following metaphor.

I could put a water pressure gauge (think of this as a voltage meter) up against a super heavy duty and primed water pump and get an amazing reading, but not know from this reading that the water tank behind that pump (the battery's amp hours) only contains 8 ounces of water and no method of replenishment, and will be exhausted in "2.7 seconds" when power is needed for a far longer duration.

Enter the important of the load test. It tests the ability for a battery to deliver charge over time and replenish itself. This is the gold standard because it reflects exactly what a battery needs to do, servicing vehicle appliances that operate over a period of time, and getting recharged over a period of time, the latter usually from an alternator.

But again, a certain poster here with the giggles not mentioning the importance of first separating the batteries before a load test or how, (and there are Stellantis "mechanics" let alone owners who don't know two batteries exist under the hood, let alone how to isolate them,) and testing those batteries independently, can, like in the voltage test, have a stronger battery cover for a weak one and fail to disclose meaningful diagnostic information.

To mock this post with no explanation runs the risk of having members think something about it isn't factual and to risk their effecting diagnostic tests (or accepting the wrongly effected tests of mechanics) in ways different from this, potentially leading to misleading results that suggest no problems when in fact there may be. I think It would be a disservice.

I don't want members stranded: not at 2AM in a deserted parking lot, not at any time on the highway because they or their mechanic misconducted a test and failed to identify problems that could easily be fixed in the safety of a shop.
 

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Jeep Wrangler JL Small battery replaced under warranty and big one? 1675264594165



I don't see what you find comedic about my sound attempt at explanation and guidance, or people not following it and risking on road problems when issues go undetected in the safety of a shop or driveway were they can be easily remedied.

Your history suggests no shortage of words when you want to make a point or disagree, and yet all you have here is the giggles: no rebuttal, no counterpoint, no difference of opinion. Don't you think the membership deserves sound guidance if that I offer is lacking and/or wrong?

Alternatively, post your laughing icon in absence of explanation, but the joke's on you.

Nearly anyone reading this knows that such repeated icons, void of attached explanation, particularly coming from someone so previously willing to offer dissent, particularly where facts warrant, are tantamount to you having issues with being corrected or having others include important points you left out (to wit: separate the batteries before tests, voltage or load.) People can see that repeated mock derision, with no content to back it up is the sham that it is.

Maybe I'm wrong. Show me here where so. I'm good with not being perfect. :)

Otherwise insert your laughing icon below Mr. @Rhinebeck01. It is, sadly, all you seem to have here void of substance to back it.
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