Another vote for the battery as a likely culprit, but a rant about it possibly not being worth your time to go to the dealer. I took delivery of my RAM in December of 2020. Dual batteries. If the truck sat for more than a few days, both batteries were so dead that no FOB would be detected, no interior light would come on. Totally dead. Computer, Radio, Commercial settings lost each time due to loss of juice. As some others have noted, when the batteries are this dead, the lithium jump starters don't work. I also have one of the very nice Battery Tenders like linked above, but they also will not initiate a charge on my batteries when they are 100% dead. I've left them plugged in for days trying to revive a totally dead battery without success. Instead, if I jump start the truck with another vehicle, and get a bit of charge, then the battery tenders can take over and maintain it when I am at home. But on the road, it is not always possible to plug the truck in each night.
Although I live more than 100 miles away from a dealer, I'm on the road a lot and have scheduled and taken it to 5 different dealers. Got @RamCares
involved, and a so-called STAR engineer involved the past two times. I've had to leave my truck (without any loaner) at dealers for weeks in total. Without loaner vehicles provided, Stellantis reimbursed only a fraction of the rental car expenses. Eventually they replaced one of the batteries, but they refused to replace the other. Despite my protestations that battery manufacturers say that discharging a lead acid battery to 0% charge a dozen times does permanent damage. With one replaced battery, my truck will now usually start after 3 days of non-use. But if it sits a week, it is still 100% dead. I can't find any parasitic draw, and I know that nothing is left on. I believe it is the second battery that is also faulty. Or possibly the UConnect system is doing something that requires a lot of amperage draw in the middle of the night that I have been unable to document.
I have pleaded with @RamCares
to simply replace that second battery. I've asked dealers to replace it. They won't. I've asked them to recontact the STAR engineer who oversaw the last week of testing, and ask them if a battery that has been drawn 100% flat a dozen times should be replaced. They won't. It is stupid that Stellantis would want a customer to hate their new truck as an unreliable, untrustworthy vehicle instead of simply replacing both suspect batteries. In principle, I want RAM to make it right. But from my experience, I have spent far more in fuel, rental cars, and time trying to get the dealerships to fix this. Clearly, in retrospect,it would have been far cheaper to just purchased two new batteries out of pocket. Especially since I'm still going to need to do this in an effort to get my truck to hold a charge for a week. So, if you are close to a dealer and can afford to be without the truck for a while - try to get the dealer to replace the batter(ies). But in my situation, I'm giving up on getting RAM/Stellantis to resolve it.