2018 JL Battery Voltage what is normal???

[Htfan]

The OP has already received great info/answers.​

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However since this question pops up continually, I'm sharing another thread I started as an additional reference:​

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https://www.jlwranglerforums.com/fo...oltage-display-for-ess-battery-health.113355/​

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[Rubi SoHo]

@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

hugely helpful, I have an e-torque, the “battery voltage” is always reading 14v. I now think I understand that this means my generator is trying (unsuccessfully) to charge a likely faulty battery, and that’s why my ESS system won’t work anymore.

 

[Steve104]

My experience, for what it’s worth:
I have a short drive to work and I looked to see that at start up the voltage of my original OEM main battery would read 12.4 (I removed the aux battery and its cables). While driving the voltage would stay a 14.5. This seemed to me to be the signs of a weak battery. So over the weekend I left it connected to my Noco 1 amp charger. The voltage on Monday morning was 12.7 and the charging while driving will be as low as 12.8 volts. (Strangely enough, the charging voltage will jump up to 14.4 when coasting in neutral.) But by the end of the week, the voltage at start up is back down to 12.4 and the charging voltage is consistently 14.5.

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