Went to start Jeep, battery dead

[Jhawth]

Measured the voltage on my main battery, everything is still hooked up as normal and I'm getting a 4.8vdc reading on my dmm. Not sure what the hell happened as last night when I drove to the gym and home it started like normal, no warning lights on the dash or anything. Pretty sure I didn't leave the electronics on after I got out, so I'm not sure how the hell the battery drained down to 4.8vdc.

Reading the owners manual says to disconnect main battery terminals before charging the battery, so going to give that a try and see if the battery holds a charge.

Anyone else experience something similar? I'm at 17xxx miles and under 2 years of ownership, would this be a warranty issue covered by a dealer?

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[Vanburi]

My experience was similar. I went to leave work for lunch and no start. Only other sign was the start stop had not been working.

 

[Fudster]

Pretty sure I didn't leave the electronics on after I got out

I beg to somewhat comedically differ Jake. In fact you potentially left the ultimate electron pig connected after you got out: a possible defective ESS battery robbing the main battery of current.

If your main battery takes a charge and this happens again you may want to recharge the main battery isolate the ESS battery from the electrical schematic of the vehicle--it is not needed--to see if the ESS battery is the culprit.

Good luck.

 

[Jhawth]

I beg to somewhat comedically differ Jake. In fact you potentially left the ultimate electron pig connected after you got out: a possible defective ESS battery robbing the main battery of current.

If your main battery takes a charge and this happens again you may want to recharge the main battery isolate the ESS battery from the electrical schematic of the vehicle--it is not needed--to see if the ESS battery is the culprit.

Good luck.

I think you may be correct that I left the ultimate electron pig connected. I did measure what I would believe to be the aux battery voltage at 3.x vdc. I had the positive and negative battery terminal clamps removed and put my DMM leads on there to get the 3.x vdc reading.

I did a little more digging on here and found a thread (https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/) about pulling the F42 fuse which is tied in with a relay for the aux battery, and disconnected the aux battery ground from the main battery. The charger only had the main battery to 11.5vdc and I couldn't wait longer so I just ended up jump starting the Jeep. Fired up no problem, no errors or warnings on the dash regarding the ess system. Drove it around for 15ish minutes no problems, in dash display battery gauge was showing 14-14.2vdc. Going to see if it starts for me tomorrow morning.

 

[Jebiruph]

I don't know if this is what happened here, but if you don't follow the correct sequence when you park, the JL is left in ACC mode and the batteries drain overnight. If I remember correctly, it happens when you are parking and push the stop button before you shift the transmission into park. This puts the ignition in ACC mode and the shifter flashes indicating it's not in park. Then after moving the shifter to park, if you don't switch the ignition from ACC to stop, the ignition stays in ACC and will eventually drain the batteries.

 

[bobcat.K5]

I am trying to chase this gremlin too. 2020 JL 4dr.

Installed taccom sun visor clips to hold the sun visors in place. Next day, the jeep wont startup. Had to jump start it. Wrote it off as a one off issue. The next day same problem.

Got the main battery/starter/alternator tested at o-reillys and they are all good.

Any ideas..

 

[2020 Rubi Diesel]

2020 JLURD and I've been chasing this issue since June 22'. I had to replace both batteries and then it started working. Then randomly, it doesn't start. I bought it with lights and a winch on it in June 21 and added RS steps/Pedal monster/Derringer/Tazer mini in November 21. Had zero issues until June 22'. I've had ESS and traction control off since the tazer install.

Since then, I have a random dead battery. I bought a trickle charger for it.

Who turns off the vehicle before shifting into park? I always shift into park first then turn it off.

I have noticed that the vehicle sometimes is "awake" hours after being off and no key fob in sight.

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