2018 JL Battery Voltage what is normal???

[jiwooncc]

my vehicle running about 70k miles now. Changed my AUX battery about 4 weeks ago and the MAIN battery about two days ago. Car seems to be running fine but with the MOPAR battery I had in my jeep Voltage shows 13.8-14.2 when driving but now that I got a new battery (Duralast Platinum H6 AGM), when I turn on the engine it stays at 12.7-12.9....... When cruising and my foot off BOTH pedals it goes up to 14.0 - 14.2 and then once I ACCELERATE or BRAKE it goes down to 12.8 ish.

Its a brand new battery and Im questioning why im seeing 12.7-12.9 and not higher.... (went to autozone and battery is perfectly fine, they said it could be the Alternator but old battery didnt start with 12.7-12.9 it was ALWAYS 13.8 - 14.2 and when auto stop start is activated then it would go down to 12.2-12.5 and when engine turns back on it goes up to 14 ish

IF 12.8 is a NORMAL VOLTAGE and shoots back up to 14.2 when cruising....... I really dont know why It goes down to 12.8 when braking or accelerating.......


ANY IDEAs?

Sponsored

 

[Reinen]

13.8-14.2v isn't from the battery. It's from the alternator trying to charge the batteries. Now that you have better batteries the alternator isn't always trying to charge them.

12.7-12.9v is a fully charged battery. So the alternator doesn't kick in and voltage will stay 12.7-12.9v.

12.2-12.5v is a slightly drained battery. So the alternator will kick in and raise the voltage to 14ish to charge them. Which would be expected after an ESS start. It's also a smart alternator which will try to kick in while you are not accelerating unless the batteries are so low that it needs to kick in regardless of your driving.

All completely normal.

 

[jiwooncc]

13.8-14.2v isn't from the battery. It's from the alternator trying to charge the batteries. Now that you have better batteries the alternator isn't always trying to charge them.

12.7-12.9v is a fully charged battery. So the alternator doesn't kick in and voltage will stay 12.7-12.9v.

12.2-12.5v is a slightly drained battery. So the alternator will kick in and raise the voltage to 14ish to charge them. Which would be expected after an ESS start. It's also a smart alternator which will try to kick in while you are not accelerating unless the batteries are so low that it needs to kick in regardless of your driving.

All completely normal.

COPY THAT. Thanks.

It was new to me with dash saying Voltage of 12.7 - 12.9 now.

I believe my MOPAR factory battery went dead after 20k and went to dealership for free charge or free replcaement under warranty. It was up until around 70k miles now that I completely went with aftermarket battery. I guess when I was using the mopar one and it always stayed around 13.8 - 14.3 that was not a good sign...? Could that be a sign that main battery is bad because alternator is trying to charge it up so its always up there with high 13 and low 14?

Im not used to seeing 12.8 12.9 on my dash with NEW battery so just a thought. Thanks though.


AND fact that when Im not ACCELERATING nor BRAKING it goes up to 14.2 and then when I BRAKE or ACCELERATE it drops to 12.8 so...... never seen the voltage go up and drop every time.... idk if thats normal. (I would only notice it go down when Im on auto stop start and goes up when engine starts up again, but NEVER when im driving and braking and accelerating...)

 

[Reinen]

COPY THAT. Thanks.

It was new to me with dash saying Voltage of 12.7 - 12.9 now.

I believe my MOPAR factory battery went dead after 20k and went to dealership for free charge or free replcaement under warranty. It was up until around 70k miles now that I completely went with aftermarket battery. I guess when I was using the mopar one and it always stayed around 13.8 - 14.3 that was not a good sign...? Could that be a sign that main battery is bad because alternator is trying to charge it up so its always up there with high 13 and low 14?

Im not used to seeing 12.8 12.9 on my dash with NEW battery so just a thought. Thanks though.


AND fact that when Im not ACCELERATING nor BRAKING it goes up to 14.2 and then when I BRAKE or ACCELERATE it drops to 12.8 so...... never seen the voltage go up and drop every time.... idk if thats normal. (I would only notice it go down when Im on auto stop start and goes up when engine starts up again, but NEVER when im driving and braking and accelerating...)

The general consensus is that Mopar batteries suck. You're just seeing why.

What you're seeing now is normal. What you were seeing before was the alternator working overtime.

 

[jiwooncc]

The general consensus is that Mopar batteries suck. You're just seeing why.

What you're seeing now is normal. What you were seeing before was the alternator working overtime.

Yeah, I thought so.

But do you think its normal for the NEW battery to act like that where it stays 12.8 and then jumps up to high 13 low 14 when cruising? and goes back down to 12.8 when accelerating

I WILL POST A VIDEO OF WHAT IT MEANS later tonight.

 

[Reinen]

It's completely normal.

12.8v is a FULLY CHARGED AGM battery. 13.8-14.3v is the alternator trying to charge the battery to 12.8v. It was likely very rare that your old crappy Mopar batteries ever reached a fully charged voltage and you saw the 13.8-14.3v from the alternator nearly all the time.

 

[RubberFrog]

You've been given the correct answer several times.

 

[Reinen]

You've been given the correct answer several times.

I was one post away from saying that. ?

 

[jiwooncc]

I was one post away from saying that. ?

thank you guys appreciate it HAHA

 

[jiwooncc]

It's completely normal.

12.8v is a FULLY CHARGED AGM battery. 13.8-14.3v is the alternator trying to charge the battery to 12.8v. It was likely very rare that your old crappy Mopar batteries ever reached a fully charged voltage and you saw the 13.8-14.3v from the alternator nearly all the time.

It's completely normal.

12.8v is a FULLY CHARGED AGM battery. 13.8-14.3v is the alternator trying to charge the battery to 12.8v. It was likely very rare that your old crappy Mopar batteries ever reached a fully charged voltage and you saw the 13.8-14.3v from the alternator nearly all the time.

Just a short video of whats happening. Hope this is normal. Did a battery test as well at autozone and it came out 100% as it should be for a new battery. Take a look at the video and let me know what you think. If this is normal all good! I just never experienced VOLTAGE going up and down every time i drive. Im so used to staying at a consistent 13.8-14.3 never went down when driving except when auto stop start is used then it would gown besides that none. If the video seems normal thats all good!

 

[Reinen]

Just a short video of whats happening.

 

[jeepoch]

@jiwooncc

Chris, the EVIC display only shows either the Alternator (or Generator if eTorque is installed), charging system's output voltage even though the description on the display says 'Battery'. Another one of those dumbed down details for the general population of drivers. The "Battery" voltage is just a faux description, it's really the vehicle's charging system's overall output 'effort'.

Regardless, the voltage shown indicates essentially 'how hard' your alternator is working to charge your batteries, not necessarily the battery's true voltage.

The unit of measure can be anything. Call it a 'kumquat' if it makes you feel any better. The higher this number, the harder your charging system is working at trying to keep your batteries charged. And again, not the instantaneous voltage at the battery terminals.

If you recall from Ohm's law "E = I x R". Voltage (E) 'electrical potential' is proportional to current (I) and resistance (R). So for a given resistive load, as current increases so will the voltage.

However, batteries have anything except a fixed resistance. The voltage they have available at any instant in time is also very dependent on not only itself (based on charge state) but also the load of all the resistive things connected to it. So it's output voltage depends on lots of things. Is your radio on? Are your headlights or other accessories on? Everything 'on' adds up as the overall load on the battery. The higher the load, the lower it's voltage (assuming a fixed current) again based on the battery's current state of charge.

But (with a capital B), the battery's charge state is always being depleted (it's overall available energy) under load is always going down. So due to Mr. Ohm's equation, your battery's voltage is always going down as well.

The only way to 'charge' the battery (while under load) is to supply enough input energy, in the form of current (the amount of moving electrons as measured in amps) to overcome not only the load of the system (all the things that are turned 'on') but also the internal resistance of the battery itself while being discharged. Not a trivial thing.

Unfortunately, the monitoring circuitry does not measure current, it only measures voltage which is just an indirect indication of charging effort. Again due to Ohm's law we can believe current is increasing as the voltage increases. Yet, the resistance across the entire system is constantly changing due in part to the charge state of the battery itself. So our monitoring mechanism is far less than optimal but by far the absolute cheapest to implement.

So as you can see, this is all somewhat complicated. But the largest loading factor in your vehicle's entire electrical system is the state of charge of it's battery. To make matters worse (in fact much, much worse) the design idiots of the ESS system decided to drop in not one but two batteries into this mix. Worse yet (much worse by even an other order of magnitude) they used two dissimilar sized batteries connected in parallel which have their own unique internal charge states and internal resistance characteristics. This presents a much, much, much more difficult charging solution. Did I mention just how moronic this configuration truly is? If not, I really should.

So in order to keep things simple, don't look at your battery readout in volts (standard electrical potential), but rather as a relative number that indicates the amount of kumquats (electrical effort, my unit naming invention) that your alternator (or generator) has to produce in order to supply enough energy to not only run everything that's turned on but also provide the additional energy to overcome each of the batteries (plural) internal resistances. [Wow, what a sentence.] Just to keep both batteries charged (or stated more accurately) in a state of active charging. The only time a battery can ever be 'fully' charged is if it's totally disconnected and under no load.

But even then, it's not a perfect machine and will leak it's charge over time due to it's own internal resistance.

Battery charging and it's charged state cannot be easily measured with a voltmeter. Stop trying to make sense of the voltage value itself. Instead think of the battery display as a bar graph where the higher the number, the harder the system is working at supplying just enough (minimal) amount of energy to try and keep the batteries sufficiently charged. The lower the value, the easier it is on your charging system (and engine) to maintain sufficiently charged batteries. This value will naturally be fairly dynamic. Since many things require constant power, the charge state of your batteries will be less at ignition on than while driving for some time.

As long as this value doesn't always remain high (in the mid to high 14 range) then your charging system is effectively doing it's job. Otherwise, your batteries are depleted to the point where they can't be charged sufficiently. Lower values, low 13 to high 12 range is a great metric for good battery health.

Remember, charging 'effort' not 'potential'. The 'kumquat' is as good as any unit of measure in this regard.

Hope this helps.
Jay

 

[swampflyer]

Out standing explanation. Well written. Even I understood. Thanks for your effort.

 

[henryb]

my jl which is a unlimited sport had no second battery its a 2021 i installed a gennis 3 dual battery system . i was unaware it had only the one battery. quite easy to do cost about $1100 i believe with two new battlers and the kit.did it for peace of mind .hearing all those horror stories of that small hidden battery giving up the ghost at any time

 

[Reinen]

Connecting batteries of different Amp Hour (AH) ratings like the JL does isn't as bad as everyone makes it out to be. It's not ideal, but it's not all that bad. AH rating actually doesn't matter at all. The batteries will drain proportionately. What matters is the resting voltage of each battery because they will always try to equalize with each other.

The voltage of two batteries that are the same size, same AH rating, same age, made by the same manufacturer are very likely to rest at the same voltage. That's why all that is recommended.

The voltage of two batteries that are different sizes, different AH ratings, made by different manufacturers are more likely to rest at slightly different voltages. But if they're both new batteries this is only slightly bad because their resting voltages will still be rather close. What ends up happening is the battery with the higher resting voltage (which could be the larger or smaller battery, AH doesn't matter) will constantly try to equalize with the battery with the lower resting voltage, which will not accept resting at that voltage. This will stress the battery with the higher resting voltage until its resting voltage is reduced to the point where it is equal to the other battery's resting voltage. But since they're both new and their resting voltages are rather close, this isn't all that much stress in the big picture of the battery's lifespan. More stress than two identical batteries are likely to have but not all that much more.

BUT the different sized dual batteries opens the door to a lot of misunderstanding and bad practices.

The #1 bad practice by far is testing the batteries and finding that one is "bad" and the other is "still good", so you only replace the "bad" battery. When it comes to batteries, "bad" and "good" mean they either test above or below an arbitrary value where they are considered too worn to operate a vehicle. It's a Pass/Fail test. But their test scores are actually like a graded test. "Bad" is an F. But "good" can be an A, B, C or D. An A grade is very different from a D grade. When you only replace the "bad" battery you end up with a new A grade battery linked with an old D grade battery. Their resting voltages will be nowhere near each other. This will severely stress the new battery and drastically reduce its lifespan. Even Jeep Dealerships will do this. It's a terrible thing to do unless you really enjoy buying batteries. (or a great thing to do if you really like selling batteries)

This bad practice gives the Aux battery a bad rap. The larger size of the Main makes it slightly better at compensating for its own inadequacies. So it's usually the Aux that tests bad first, even though the Main is not far behind. Once the Aux gets replaced the older main severely stresses the new Aux battery and the Aux dies really fast, constantly compensating for the older main. Again the "stupid Aux" battery gets the blame for it when it's really bad practices leaving your older Main battery in place, allowing it to destroy any new battery it gets paired with. Small, identical or larger.

So always replace both Main and Aux at the same time so their resting voltages are as close as possible. Don't worry that they're different sizes, identically sized batteries are only slightly better. It's still light years better than linking an old and new battery.

Sponsored