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Discussion Starter · #1 ·
Hi all,

I had a quick question. I read through a lot of the battery threads already but didn’t seem to understand something. I just replaced my battery 2 days ago which was the original battery in 2020 Pacifica touring L plus. Now the ESS light came on saying my system is not working (could be aux battery)? Which I’m taking to the dealer tomorrow.

However, when the new battery was put in I noticed my voltage was always 13.8 while running. This morning however it hovered around 12.6 while running and would go up to 13.8 when I decelerated off the pedal, and back to 12.6 while running and at idle. What does this actually mean and is this a problem I need to look into further? Thank you for all your help.
 

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2018 Pacifica Touring L + S
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The display on the screen when the engine is running is showing the output of the charging system. Not the battery voltage. If you only had one battery tested/replaced, the other may have been weak also. And if not replaced, it will bring down your new main battery again. Make sure both batteries are tested while the negative connection to the aux battery is disconnected.
 

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Discussion Starter · #3 ·
The display on the screen when the engine is running is showing the output of the charging system. Not the battery voltage. If you only had one battery tested/replaced, the other may have been weak also. And if not replaced, it will bring down your new main battery again. Make sure both batteries are tested while the negative connection to the aux battery is disconnected.
thanks. Why do we have to test the batteries with the aux disconnected?
 

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Discussion Starter · #4 ·
The display on the screen when the engine is running is showing the output of the charging system. Not the battery voltage. If you only had one battery tested/replaced, the other may have been weak also. And if not replaced, it will bring down your new main battery again. Make sure both batteries are tested while the negative connection to the aux battery is disconnected.
Also is it normal for the voltage to fluctuate will on and off the gas pedal? My understanding is less voltage is needed when accelerating so my voltage drops down to 12.6 bc the alternator is charging it. Is the voltage always supposed to stay constant at 13.8? Thanks
 

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With the batteries connected, you are testing the total of the two batteries instead of the individual batteries. So one low battery will seem to be OK because of the power from the good battery.

The voltage will fluctuate for different reasons. Your air conditioning kicks in, or a fan starts, or any other electrical load starts or stops.
 

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Discussion Starter · #6 ·
With the batteries connected, you are testing the total of the two batteries instead of the individual batteries. So one low battery will seem to be OK because of the power from the good battery.

The voltage will fluctuate for different reasons. Your air conditioning kicks in, or a fan starts, or any other electrical load starts or stops.
thank you. I just had a couple of questions for my better understanding.

1) what indicates a better healthier battery? If the reading on the dash cluster of voltage is higher or lower in general?

2) any particular reason my voltage would go from constantly reading 13.8v the first couple of days I replaced the battery while driving to now fluctuating up and down between 12.6 and 13.9v depending on accelerating or decelerating?

i am set to take my car in to check out the aux battery tomorrow. Thanks
 

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surprised you changed batteries on a 2020. My 2017 is still running on original. The aux was changed after 3 years 9 months. My voltage is 14.1 14.5... most of the time. When my aux went bad it was 14.6 14.9 all the time.
 

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Discussion Starter · #8 ·
surprised you changed batteries on a 2020. My 2017 is still running on original. The aux was changed after 3 years 9 months. My voltage is 14.1 14.5... most of the time. When my aux went bad it was 14.6 14.9 all the time.
yea got it in 2019 so about 2 years (can be normal for az batteries here). When the voltage is over 14 or higher does that mean battery is on its way out?
 

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yea got it in 2019 so about 2 years (can be normal for az batteries here). When the voltage is over 14 or higher does that mean battery is on its way out?
I don't think so. Mine has always been in the low 14s high 13s. However when AUX went bad, I noticed charging in high 14s... I imagine that is what kills the main if you don't change that AUX battery when your @ light comes on.
 
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