My Aux v Main Battery Experience

[Keiland]

Thought I'd throw my 1.5 cents in for the record in case anyone runs into same. Daughter #2 (19) ran down the battery parked in the DQ parking lot w lights on and radio on, then needed a jump (kids! ). Since then, slightly sluggish cranking & ESS Stop/start stopped working ("battery protection mode"). Volts reading a constant 14.3-14.4 while driving. After reading bunch o' threads here I figured it was the Aux battery but went ahead & bought an Interstate aux & main battery as the JL is 4 years old (w 40k otherwise problem-free miles). I started off removing fender & replacing the aux, which didn't change anything. Put in the new main battery, and all was fixed and working correctly.

I tested the old batteries After removing & the old aux was actually still decent reading 12.6, however old main read 11 .6v.

Only reason I post is the aux is frequently seen as the culprit w the ESS start/stop canary in the battery coal mine, but in this case, it was just the main battery causing that symptom. It's even possible the aux was compensating for the bad main? I probably could have figured that out by isolating and testing each beforehand, but figured was time for two new batteries anyways. Who knows how long the originals would've lasted had the "DQ incident" never occurred, but hey that's life! Hope this minor experience helps someone else who's stranded out there one day!

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[Rhinebeck01]

Thought I'd throw my 1.5 cents in for the record in case anyone runs into same. Daughter #2 (19) ran down the battery parked in the DQ parking lot w lights on and radio on, then needed a jump (kids! ). Since then, slightly sluggish cranking & ESS Stop/start stopped working ("battery protection mode"). Volts reading a constant 14.3-14.4 while driving. After reading bunch o' threads here I figured it was the Aux battery but went ahead & bought an Interstate aux & main battery as the JL is 4 years old (w 40k otherwise problem-free miles). I started off removing fender & replacing the aux, which didn't change anything. Put in the new main battery, and all was fixed and working correctly.

I tested the old batteries After removing & the old aux was actually still decent reading 12.6, however old main read 11 .6v.

Only reason I post is the aux is frequently seen as the culprit w the ESS start/stop canary in the battery coal mine, but in this case, it was just the main battery causing that symptom. It's even possible the aux was compensating for the bad main? I probably could have figured that out by isolating and testing each beforehand, but figured was time for two new batteries anyways. Who knows how long the originals would've lasted had the "DQ incident" never occurred, but hey that's life! Hope this minor experience helps someone else who's stranded out there one day!

Without proper load testing of the separated batteries (2) you really do not know the status of each battery.

Regarding your 2018 JL with dual battery system..... reality is, both of those factory batteries it had were long in the tooth / had aged out and were due for replacement.

Better move would be to have replaced them both at the same time. Regardless, good you did replace both batteries.

 

[Keiland]

Thanks! I only drove around the block (maybe 2 mins) with the new aux/old main, just to see if it changed the volt reading. Then I put in the new main. Kind of a dopey move on my part...Hopefully that didn't stress out the new aux too much. It all seems to be working fine now. Next time I'll know exactly what to do!

 

[Jebiruph]

Thought I'd throw my 1.5 cents in for the record in case anyone runs into same. Daughter #2 (19) ran down the battery parked in the DQ parking lot w lights on and radio on, then needed a jump (kids! ). Since then, slightly sluggish cranking & ESS Stop/start stopped working ("battery protection mode"). Volts reading a constant 14.3-14.4 while driving. After reading bunch o' threads here I figured it was the Aux battery but went ahead & bought an Interstate aux & main battery as the JL is 4 years old (w 40k otherwise problem-free miles). I started off removing fender & replacing the aux, which didn't change anything. Put in the new main battery, and all was fixed and working correctly.

I tested the old batteries After removing & the old aux was actually still decent reading 12.6, however old main read 11 .6v.

Only reason I post is the aux is frequently seen as the culprit w the ESS start/stop canary in the battery coal mine, but in this case, it was just the main battery causing that symptom. It's even possible the aux was compensating for the bad main? I probably could have figured that out by isolating and testing each beforehand, but figured was time for two new batteries anyways. Who knows how long the originals would've lasted had the "DQ incident" never occurred, but hey that's life! Hope this minor experience helps someone else who's stranded out there one day!

I think that if more people checked like you did, they would find that the aux battery does not fail as often as every one believes. If you still have them, I would have both batteries load tested to help confirm their condition.

 

[Jephson]

@Jebiruph, thanks for all your info here. Back in July 2022 I had a catastrophic JL ESS failure in the middle of a busy road (2019 JUL). I poured over this forum and found that my aux had failed, the main battery had been drained and the N3 fuse had blown. Replaced all three and was good as new till the big Christmas cold snap. I'm now getting consistently 14.4 volts on my 6 month old battery on the Jeep display. The voltmeter reads 12.56 on the battery and the aux seems to work fine. When stop/start is engaged at a stop, the voltage falls to 12.5 and then it jumps up to 14.1-14.4 when driving. I have a Tazer on order and will install that and disconnect the negative aux cable, but any thoughts about what else might be going on?

 

[Jebiruph]

@Jebiruph, thanks for all your info here. Back in July 2022 I had a catastrophic JL ESS failure in the middle of a busy road (2019 JUL). I poured over this forum and found that my aux had failed, the main battery had been drained and the N3 fuse had blown. Replaced all three and was good as new till the big Christmas cold snap. I'm now getting consistently 14.4 volts on my 6 month old battery on the Jeep display. The voltmeter reads 12.56 on the battery and the aux seems to work fine. When stop/start is engaged at a stop, the voltage falls to 12.5 and then it jumps up to 14.1-14.4 when driving. I have a Tazer on order and will install that and disconnect the negative aux cable, but any thoughts about what else might be going on?

It seems normal to me, cold weather affects battery performance and subsequent charging rates.

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