Jumped Main Battery/Now have warning

[tonyt]

I shut my 2021 Mohave off and left it in park. That let the battery run down. I jumped it with a jump box, main battery is fine, but the secondary battery isn’t working. I get the notification that the stop/start system is not working, but the main battery stays fine and fully charged. If the aux battery is bad doesn’t that run your main battery down?
Can’t figure out what’s going on.
Any help would be appreciated!
TonyT

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[sharpsicle]

That warning doesn't necessarily mean the aux battery is bad. There's a myriad of conditions that must be met for auto stop/start to work. What message are you getting exactly?

Also, did you test the aux battery? What is it reading?

 

[tonyt]

No I haven’t. Not very auto electricly talented LOL. Not very auto anything talented. Basic skill level.

 

[sharpsicle]

How about the exact message the EVIC is giving you regarding the auto stop/start? You might just have batteries that need to charge up before it works again.

 

[tonyt]

It says “Start/Stop system unavailable. Service Start/Stop System.

 

[sharpsicle]

Yeah, you'd need to test the components of the system. You might have a bad battery, might have a blown fuse, might have a bad sensor somewhere. My bet is both batteries need to be replaced. If you're not electrically inclined I would start by taking the batteries to a local parts store for a load test.

 

[Rusty PW]

Charge both batteries separately. Leave sit overnight after charging. Use volt meter to check voltage on each battery. If less then 12.2 volts. Battery is on it's way out.

 

[Badunit]

Shutting off your Jeep and leaving it in park is normal operation, not something that would typically run the batteries down unless it was unused for months or one of the batteries was going bad.

Unfortunately all of the suggestions require some knowledge of the electrical/battery system and some mechanical ability. It is not a simple task to remove the Aux battery and take it to a shop for testing, it is buried behind the fender liner. Even removing and resinstalling the main battery can cause major problems if one is not careful; you can blow some of the major fuses.

You need to take it to a shop. It is probable the aux battery is bad and has damaged the main battery by draining it. The shop can figure that out and fix whatever needs fixing.

 

[Medical_Bartender]

I just replaced my main battery (2022 gladiator) and disabled the auxiliary a month or so ago. Yours being a 2021 I'd imagine the batteries are on their last leg anyway.

If you aren't auto/electrically savvy and have no desire to learn then I'd recommend finding a reputable shop in your area like the post above me suggested. It's far too easy to have one of the leads touch something or be incorrectly positioned and cause a mess of electrical issues in these vehicles. Something you can easily do is check the fuses though. If you open the fuse box under the hood (passenger side next to the battery) you'll find them all, along with a schematic under the top over of the box. There is a fuse puller in the box as well.

Good luck.

 

[tonyt]

Thanks for the comments!

 

[alpineovernappa]

It’s good practice to put any vehicle (especially these with undersized aux batteries) on a smart charger once a quarter or so if possible. A $30 battery charger overnight will help prolong the battery life significantly.

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