For years I've been fighting with both of my diesel trucks, particularly this one. In 1239 miles I've had 5 sets of batteries, and the dealer has replaced the alternator 7 times.
I don't use the truck daily, its only here to haul my toys around, I use it to tow my boat, my camper, and a few small trailers. In 16 years its not been driven more than 10 hours, but when it does go out, it runs for at least an hour or so.
This morning I took a 2 hour ride with it to pickup a free boat trailer in MD. I went out around 6am, pulled it out of the garage and let it warm up, then headed out. It sat there for about an hour, plus two stops to eat and top off the fuel along the way. I got home around 3pm. I parked the truck and did a few things to the new boat trailer in the garage. It looked like rain so I went to pull the truck into the garage, and its dead, both batteries are stone dead. Not low, completely dead.
The truck is bone stock, no accessories, nothing plugged in. Both batteries are less than 3 months old, as is the alternator. (I've got shelf full of supposedly 'bad' alternators off this and my other two trucks that were likely replaced for no reason). I ran an extension cord out and the batteries are charging back up.
Every time the batteries will charge right back up, and likely be fine for another month, or more. Then all at once they'll be stone dead again. The truck gets parked with a battery maintenance minder which I plug in roughly once a week but its never made any difference. When they go dead, there's no draw, nothing that doesn't belong there. Its as if it's not capable of maintaining its batteries on its own, If I let it sit more than three or four days without a charger on it, it goes dead, regardless of use.
The alternator is charging at 14.4 volts, the battery draw is .23 amps, (Less than the draw on my car battery), and load tests at 111.5 amps at idle.
The batteries are 3 month old OEM Motorcraft, the last set were Interstate, (put in by a dealer in MO), before that a set of Duralast batteries because they died 100 miles from home two years ago.each time, the batteries charged right up and tested fine. The part that gets me is that its done this repeatedly. The last time I died, I had just come home from an hour drive, I stopped down by the road to talk to a neighbor, I shut the truck off for 5 minutes, and it started right back up just fine, I pulled up the garage, shut the truck off to go open the door, I walked around came back out through the open door and the batteries were stone dead? zero volts, nada, nothing. The same thing it did today, only today it had two hours to sit after I shut it off last.
Except for one time, its only done this at home, the one time it did it away from home, I was at my old place, making the last trip of the move from PA. I had shut it off to make one last walk through and went back out and it was completely dead. At that time I had no means to jump start it or charge it so I was forced to go to Walmart and buy a pair of batteries. When I got home, the two completely dead batteries charged right back up over night.
Its also only done this once in the winter, it happens more often in the warm weather. Once I get it started again today, I likely won't need it for another few weeks.
I don't think the battery minder makes any difference, its died just as often after a long ride as after sitting. Before today, I last drove it about a week ago but only for a few miles across town and back.

If it were a draw, it would have to be massive, like the glow plugs or bigger but for it to be fine one minute and completely dead the next don't make sense.
The truck is like new, its been garage kept since new, as has my other 03 F250, (I have two, both have under 10K on them). Both have had these issues over the years. I've bought four brands of battery tenders, dozens of batteries, and dozens of alternators. Through all this, my 1985 F150 starts every time no matter how long it sits. It just turned 1700 miles.

This issue started right from the start of buying the first truck, I brought it home, went to FL for the winter and came home to a dead truck. They towed it in with 12 miles on it and replaced the batteries and alternator. I drove it home, and a month later it was dead again. The second truck belonged to a relative who passed, it has less miles but has had the same issues.
Last year I bought a new Powerstroke, it too has the same issues, it can't seem to sit for more than 2 weeks without going dead.

Is it the batteries or the trucks?