Is a supplemental/ESS/aux battery jumpstart dangerous?

Jebiruph

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A few days ago a picture was posted on another thread (https://www.jlwranglerforums.com/fo...ressed-in-user-guide.40684/page-6#post-922367) that showed a jump start related addendum to the owners manual that states "Only use the positive battery post on the main battery to jump start your vehicle. Serious injury or death could result if you attempt to jump start using the supplemental battery".

I've been trying to figure out what they are referring to. Given the reference to only using the positive battery post on the main battery to jump start, I wonder if the warning applies to a suggestion I saw to jump start using the N1 terminal instead of the main battery positive. Even then, how would that result in death? They might be concerned about applying to high of a voltage to the smaller battery, but my JL alternator is charging at 14.5 volts all the time, are there jump starters that are significantly higher than 14.5 volts?

Does anyone have any insight into what the actual issue is they are warning about?
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jeepdabest

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A few days ago a picture was posted on another thread (https://www.jlwranglerforums.com/fo...ressed-in-user-guide.40684/page-6#post-922367) that showed a jump start related addendum to the owners manual that states "Only use the positive battery post on the main battery to jump start your vehicle. Serious injury or death could result if you attempt to jump start using the supplemental battery".

I've been trying to figure out what they are referring to. Given the reference to only using the positive battery post on the main battery to jump start, I wonder if the warning applies to a suggestion I saw to jump starting using the N1 terminal instead of the main battery positive. Even then, how would that result in death? They might be concerned about applying to high of a voltage to the smaller battery, but my JL alternator is charging at 14.5 volts all the time, are there jump starters that are significantly higher than 14.5 volts?

Does anyone have any insight into what the actual issue is they are warning about?
My alternator changes voltage for charge depending on battery state of charge. What has Jeep told you about yours?
 
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Jebiruph

Jebiruph

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My alternator changes voltage for charge depending on battery state of charge. What has Jeep told you about yours?
My local service dept said not to worry until it hits 14.8 volts, which it has at times, but I'm not worried about it.
 

four low

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I think they are worried about amperage, not voltage. Jump starting with battery packs, plug in hi amp chargers could overload the aux battery, the main battery can handle the amperage
 
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Jebiruph

Jebiruph

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I think they are worried about amperage, not voltage. Jump starting with battery packs, plug in hi amp chargers could overload the aux battery, the main battery can handle the amperage
Thanks for the reply. I'm not intending to pick on your reply, just raising some questions. Higher amps means higher voltage. The aux battery is rated at 200 CCA, what's the acceptable charging/boosting amps? My alternator is already charging the aux battery at over 14.5 volts.

Suppose the reason for the jump is that the main battery failed due to an internal open circuit, 0 amps into or out of the battery. Since the aux battery positive is connected to the main battery positive, wouldn't any high amp charging/boosting current connected to the main battery positive all go the aux battery - risking injury or death?

Again not picking on you, I'm hoping a group discussion might figure something out.
 

four low

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Don't worry about "picking on " me,, anything and everything that I can learn about these systems is useful information, however it is learned
 

jeepdabest

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Thanks for the reply. I'm not intending to pick on your reply, just raising some questions. Higher amps means higher voltage. The aux battery is rated at 200 CCA, what's the acceptable charging/boosting amps? My alternator is already charging the aux battery at over 14.5 volts.

Suppose the reason for the jump is that the main battery failed due to an internal open circuit, 0 amps into or out of the battery. Since the aux battery positive is connected to the main battery positive, wouldn't any high amp charging/boosting current connected to the main battery positive all go the aux battery - risking injury or death?

Again not picking on you, I'm hoping a group discussion might figure something out.
Here is charging warning on aux battery:
Thanks for the reply. I'm not intending to pick on your reply, just raising some questions. Higher amps means higher voltage. The aux battery is rated at 200 CCA, what's the acceptable charging/boosting amps? My alternator is already charging the aux battery at over 14.5 volts.

Suppose the reason for the jump is that the main battery failed due to an internal open circuit, 0 amps into or out of the battery. Since the aux battery positive is connected to the main battery positive, wouldn't any high amp charging/boosting current connected to the main battery positive all go the aux battery - risking injury or death?

Again not picking on you, I'm hoping a group discussion might figure something out.
Here are the aux battery stats:
ESS battery pic.jpg
 
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Jebiruph

Jebiruph

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Here is charging warning on aux battery:

Here are the aux battery stats:
ESS battery pic.jpg
Thanks for posting the pic. I have that picture, but never noticed it showed the charging voltage. So when my alternator is charging at 14.5 volts, it's exceeding the charge voltage limit of the aux battery. That may be an important clue as to the reason for the frequent failures of the aux batteries. I wonder why the service writer at my dealer said up to 14.8 volts is OK.
 

ToolMan514

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This issue is likely related to how heavy the gauge of wire between the main battery and the starter is. I haven't looked myself, but it is probably a lot heavier than the wires between the main and aux batteries. Connecting the jumpers to the aux would draw high amps back through the power distribution box to the main battery and then to the starter. Since it's kind of hard to get to the positive pole of the aux battery, that should not be an issue.

And as was said above, it's best to just attach the jumpers for a few minutes and let both batteries come up to voltage before trying to start the Jeep.
 

Jelllo

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Thanks for posting the pic. I have that picture, but never noticed it showed the charging voltage. So when my alternator is charging at 14.5 volts, it's exceeding the charge voltage limit of the aux battery. That may be an important clue as to the reason for the frequent failures of the aux batteries. I wonder why the service writer at my dealer said up to 14.8 volts is OK.
My charging voltage averages about 14.6V which I thought was a bit high so I went searching for what is acceptable. On the Optima battery site, for a AGM battery, I found the following info.
Recommended charging information:
  • Alternator:
    • 13.65 to 15.0 volts, no amperage limit.
  • Battery Charger:
    • 13.8 to 15.0 volts, 10 amps maximum, approximately for six to twelve hours.
 

jeepdabest

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My charging voltage averages about 14.6V which I thought was a bit high so I went searching for what is acceptable. On the Optima battery site, for a AGM battery, I found the following info.
Recommended charging information:
  • Alternator:
    • 13.65 to 15.0 volts, no amperage limit.
  • Battery Charger:
    • 13.8 to 15.0 volts, 10 amps maximum, approximately for six to twelve hours.
Unfortunately, the manufacturer of the AGM battery that is in the JL says lower voltage is required. It's a disgrace that the battery is not viewable from the engine compartment without major work and Jeep does not warn us about that in the manual or with a sticker in the engine compartment.
 

Jelllo

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Unfortunately, the manufacturer of the AGM battery that is in the JL says lower voltage is required. It's a disgrace that the battery is not viewable from the engine compartment without major work and Jeep does not warn us about that in the manual or with a sticker in the engine compartment.
Yes 14.4V is printed on the battery, but doesn't it seem strange that every other battery manufacturer states that 14.8 to 15V is the maximum for an AGM? AND the maximum charging voltage for a gel cell is 14.4V

Besides what is more important is heat. That is what is killing our batteries. The under hood temps are way too high.
 
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Jebiruph

Jebiruph

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Here's some more thoughts, I'm tending to agree that the warning is related too much current/ too high of voltage to the aux battery.

If you remove the positive terminal from the main battery, the jeep seems to easily start off of the aux battery. I don't think the issue is starting with just the aux battery and it looks like the wiring is sized for this, so I don't think is a wiring capacity issue.

Regarding jump starting using the N1 terminal instead of the main battery terminal, here's a diagram (not to scale) with a blue dashed line showing the electrical path from N1 (B) to the starter. If you jump start connected to the main battery terminal (A), the majority of the current will go to the nearby starter and the electrical resistance in the wires leading to the aux battery will reduce the current leading to the aux battery. If you jump start from the N1 terminal (B), all the current gets to the aux battery before it can get to the starter and depending on the power of the jump start, it might expose the aux battery to excessive current. Technically, this is not jump starting using just the aux battery, but at this point I think it is what the warning refers to.
underhood N1 to starter.PNG

And finally, other FCA vehicles use a similar two battery ESS system and in the Grand Cherokee, both batteries sit under the passenger seat. I wonder if the warning of injury or death might be based more on the batteries in the Grand Cherokee and then generically applied to the Wrangler.
 
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