I was a very early dead battery casualty(thread below). I had these exact symptoms. Came outside to a dead battery one day, got it jump-started after trying multiple options, finally had it sit next to a running car on jump cables for about 20 minutes. After that, I had low voltage when driving, anywhere in between 12.8 to 13.8 volts. Sometimes when I took my foot off the gas and coasted, it would go up to 14.5 for a little while, then drop back down when I hit the gas or on its own after 10 seconds or so.
I went to multiple dealerships who either didn't have batteries in stock or couldn't see me for a week or two. I said screw it. Instead of waiting for a dealership to get an appointment around Christmas time, I went to AutoZone and bought batteries myself.
I have not had any of these voltage issues since, the lowest I'll see is usually 14.1, but generally always 14.5-14.5. It will drop to 14.1 sometimes, but I'm tihnking this is only when the A/C is working fairly hard.
I'm not saying this is the solution and everyone should go by their own, but it worked for me. I've seen people with dealers replacing batteries multiple times, I have not had that issue.
I've seen many have had the dead battery or battery drain issue. I noticed my truck had the dash still on about 30 minutes after I ha locked the truck with the key nowhere nearby. Woke up this morning to a dead truck. Does anybody have a service report from their fix or any other information...
www.ram-rho.com
Another note, in terms of installation, I disconnected the main battery, then aux and installed the aux, then the main. No special sequence, just what made the most sense since the aux is buried behind the main.
Also, I saw someone post about a warranty fear, I don't think buying a non-Mopar battery can void warranty, similar to how using non-Mopar oil won't void your warranty, as long as it meets spec. Plus, the burden is on them to prove your battery caused issues.
There's my 2 cents/experience.