Yet another voltage, ESS, dual battery issue/question

[plisken]

I know there are a multitude of dual battery, ESS and voltage threads but anyway, here’s the deal, I’ve had the Jeep from the end of June but due to a few issues (mainly an alarm issue), she was in the dealers for almost two months, so I don’t have a great deal of miles under my belt. She is a 2020 Rubicon with 8000 miles or so and I feel as though there is something not quite right with the battery, batteries or the charging system.

The stop/start system only worked intermittently when I got the car and did on at least once occasion show the Service Stop/Start system fault. As this is a UK car, there is apparently no stop/start menu feature, so there is no way to find out why the system would not engage under normal circumstances.

Anyway…

When driving, the voltage normally shows 14.4v +/- 0.1v and when the stop/start system engages, it drops pretty quickly to 12.1v (haven’t yet seen it drop below 12.1).

If I’m sitting in the car, with the radio on perhaps but the engine not running, I can observe the voltage and it also drops to 12.1 volts, albeit at a slightly slower rate than if the stop/start had engaged.

I have never seen the driving voltage increase when I am coasting and similarly, never seen it reduce when on the power, it is almost always around 14.4v. The only exception to that would be after maybe after a couple of consecutive runs (20 miles), where it would perhaps drop towards the 14.2v mark.

It may be worth noting that recently, even though the voltage showing when driving is 14.4v, the stop/start seems to be working as expected.
In the past, I would consider anything greater than 14v while the engine was running to be good but similarly, have read that this should not be the case with these Jeeps.

Anyway, thoughts would be appreciated. I’m not so keen on going back to the dealers yet again, given the time it took to diagnose my previous problem, not to mention the wait for the replacement part. I'd much rather just go out and buy two batteries and replace them, if I knew beyond doubt that they were suspect and part numbers (specifically for the small one).

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[longfiredragon]

It sounds like it is now working normally? What's the issue?

Remember the ESS takes data from all kinds of stuff, like inside temp. of the jeep, RPM, engine temp. etc. if all parameters are not met, it will not engage. If all parameters are met it will engage. Another words sometimes if it doesn't engage, it's ok, it's just that something is not within the parameters.

 

[plisken]

It sounds like it is now working normally? What's the issue?

Sorry, I'm concerned over the constant 14.4v reading, where others have reported this fluctuating depending on charge and driving conditions, higher when coasting and lower when on power.

 

[Chupacabra]

Sorry, I'm concerned over the constant 14.4v reading, where others have reported this fluctuating depending on charge and driving conditions, higher when coasting and lower when on power.

I watched mine like a hawk when my ESS just randomly stopped working. It's usually around 13.9-14.1 on mine, occasionally as high as 14.2 but I'd say the average is right at 14.0.

Putting a battery tender on mine overnight seemed to "top off" the batteries and my ESS has worked as expected ever since. Been almost a month and no more issues with it.

 

[plisken]

I watched mine like a hawk when my ESS just randomly stopped working.

What sort of voltage were you seeing when your ESS wasn't working?

Do you see the voltage increase when coasting v decrease when on the power or are you seeing 13.9-14.1 regardless?

 

[Htfan]

The battery tender is a very good idea.

Have you checked each battery's voltage individually at rest? I would guess one or both are weak. In my case, the small Aux battery was compromised and draining the main battery. Fast forward to today, I've replaced both batteries.

Regular voltage between 12.7v and 13.2v while driving and only temporarily increases above that while coasting.

 

[plisken]

Have you checked each battery's voltage individually at rest?

I haven't but will do, know it's not as simple as measuring across the main battery and didn't like the thought of removing the fuse box to get at the small one.

The thing is, I'm edging towards my small battery drawing the main one down as when it was previously in the dealers for stop/start issues, they reported that they charged the battery, something I thought strange at the time. It's under warranty, just replace the damn thing(s).

I'll check individual voltages at rest...

 

[Htfan]

I haven't but will do, know it's not as simple as measuring across the main battery and didn't like the thought of removing the fuse box to get at the small one.

The thing is, I'm edging towards my small battery drawing the main one down as when it was previously in the dealers for stop/start issues, they reported that they charged the battery, something I thought strange at the time. It's under warranty, just replace the damn thing(s).

I'll check individual voltages at rest...

You can isolate the batteries simply by removing the Aux battery ground from the main battery terminal.

 

[Htfan]

Here's an image of my old battery with a quick disconnect on the Aux battery ground.

 

[plisken]

You can isolate the batteries simply by removing the Aux battery ground from the main battery terminal.

Just so I'm clear, if I remove ONLY the Aux battery ground from the main battery terminal, can I then;

• measure the voltage of the Aux battery ONLY by measuring across N1 and the removed ground?
• measure the voltage across the main battery as I would normally do, from positive to negative or ground?

Thanks

 

[Htfan]

Just so I'm clear, if I remove ONLY the Aux battery ground from the main battery terminal, can I then;

• measure the voltage of the Aux battery ONLY by measuring across N1 and the removed ground?
• measure the voltage across the main battery as I would normally do, from positive to negative or ground?

Thanks

Your methods above will work for each battery's voltage. Also, a simplified version for testing the Aux battery is positive of main battery (connected to Aux battery positive when ESS not engaged) and removed Aux battery ground.

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