Problem after installing both batteries

[TonyM]

I have a 2018 JL Sahara with tow package. I preemptively decided to replace both batteries yesterday. Everything went smoothly. Jeep was charging at 14 volts while running. Battery was 12.5 volts with engine off. This morning. The battery was 12.5 before starting but now when engine is running volts are 12.7. Took it for a short spin and while accelerating volts are at 12.7 but when deaccelerating the volts go up to 13.5. Is my alternator going out?

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[melendez69]

Tough to say whether or not your alternator is the problem. What was the behavior prior to the battery swap? How good where the replacement batteries?

Check for loose grounds... I had similar behavior a couple weeks ago and I had a loose ground. Whatever you do... don't go pushing all fuses in...because... well... nevermind.

Someone much more experienced than I am may have a more qualified opinion.

 

[TonyM]

Replace with duralast. Alternator was charging at 14 volts before swap. I will check grounds.

 

[Vanburi]

It is likely due to the previous batteries being weak and needing more charge. The new batteries are good and require less alternator input...

 

[Chupacabra]

There's also a slight chance you blew that big fuse on the side of the fusebox if you weren't really careful. Since both batteries are always connected you have to be very careful to not let the positives touch anything when replacing either battery unless you completely disconnected both grounds at the IBS.

 

[TonyM]

thanks. What would be a sign of blowing the big fuse? Would it throw an error message? I may order the fuse just to have on hand. I see there is two and I need one for tow package.

 

[NULL POINTER]

thanks. What would be a sign of blowing the big fuse? Would it throw an error message? I may order the fuse just to have on hand. I see there is two and I need one for tow package.

Part numbers listed in this post... https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/post-1867002 " IF you have the tow package you need to use 68368854AA Mopar Z Case Fuse Array " courtesy of @Rhinebeck01 Always good to keep a spare one of these in your jeep.

 

[Bob Burd]

You didn't blow any fuse. That's completely expected behavior of the smart alternator after installing fully charged batteries.

 

[Rhinebeck01]

Part numbers listed in this post... https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/post-1867002 " IF you have the tow package you need to use 68368854AA Mopar Z Case Fuse Array " courtesy of @Rhinebeck01 Always good to keep a spare one of these in your jeep.

While it does make sense to have a spare high amp fuse array.... in regard to the OP's JL, I am very doubtful his JL's high amp fuse array has issues....

Op @TonyM 's JL appears to be exhibiting very normal behavior right now. Do research IBS Sensor and the JL/JT.

 

[The Fixer]

It is likely due to the previous batteries being weak and needing more charge. The new batteries are good and require less alternator input...

Agreed. My wife's '18 JLU behaves the same way, we installed 2 new Duralast batteries last summer. The smart alternator is doing it's job.

 

[HiJinx69]

I replaced both batteries last month. I also noticed fluctuations with the voltage, previously it always held at around 14V. I took it in to the dealer to have it checked. It all checked out, fluctuations are normal. Downside, the auto start/stop is working again. Before with the weak battery, it never kicked in because the alternator was always at peak charging.

 

[Maydaygray]

I had the same issue. Replaced both batteries. Had Autozone do their test and they said it was a bad alternator voltage regulator. Bought 240 amp Duralast alternator - same exact readings! But my Battery Tender 4 amp still takes 1-3 hours to top off my batteries even after driving for several hours. Worried something else is wrong. OR I guess I just have a "new" alternator!

 

[TonyM]

I had the same issue. Replaced both batteries. Had Autozone do their test and they said it was a bad alternator voltage regulator. Bought 240 amp Duralast alternator - same exact readings! But my Battery Tender 4 amp still takes 1-3 hours to top off my batteries even after driving for several hours. Worried something else is wrong. OR I guess I just have a "new" alternator!

Today after sitting for a day the alternator started charging at 14 volts. At this point I will hold off on changing the z fuse bus unless the start stop fails or the main battery starts to get low.

 

[redsyphon]

As far as the 12.7 to 13ish when decelerating, mine does this when the batteries are fully charged (i.e. 12.7 from the nator).

I think it's by design and I've always just assumed it had to do with the auto stop/start system (even when disabled).

I'd say if you're not seeing any electrical issues or odd driving/bad engine performance, then you're probably good. Though, I also carry a spare fuse panel as it's just cheap insurance that lives in the glove box.

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