Dead Battery - Electrical Chaos

[L06An_5]

Just a quick FYI on my recent dead battery experience. I have a 21’ Willys JLU 3.6 eTorque, no small battery, but we do have the 12v and a 48v battery in the back. I do have a custom alarm system which does cause an ongoing power draw and some other electrical mods. I am not concerned about the power draw.

My Jeep sat for about two and a half weeks, I used the remote unlock it, it clicked but didn’t unlock. I used the key and was immediately thinking drained battery. Interior lights came on but were dim, I then went to start it, had to put the fob to the start button... that’s when electrical chaos ensued… wipers started “trying” to go, dash started flashing it wasn’t in park, which it was, relays in the engine compartment started clicking, lights flashing then browning out. No matter what I did I couldn’t turn it off because according to the system it wasn’t in Park.

So, I popped the hood, disconnected the ground from the battery and put the battery on a charger overnight. Reconnected in the morning and all good, no issues.

I will note that some have speculated the 48v battery would allow you to start the Jeep, not so in my case. I do believe the 48v was good since once I got the jeep started the ESS didn’t go into charging mode and worked fine immediately.

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[Heimkehr]

A 2021 vehicle is still a bit too new, in terms of reasonable battery life, to suspect the 12V battery to be the source of your electrical gremlins. However, what you describe, and experienced, is in fact the exemplar of that very thing possibly occurring: a 12V battery that is seemingly close to, or at, the end of its practical service life.

What is the battery's resting voltage? What does that number drop to when cranking the engine? The former can appear to be a good value, e.g., 12.3V, but then fall off a cliff during a starting event. Having those two figures might provide good intel when deciding whether or not to replace the 12V battery as a prophylactic measure, if not out of actual necessity.