My truck keeps dying...I've gone through 3 batteries in 3 years. After sitting a few days, the battery is dead. If it sits in the cold, it's dead by morning.
The battery tests at 12.8 volts when fully charged, and I can see it dropping .01 volts every 10 seconds or so while I look at the voltage tester.

I replaced the radio, but no change.

Remote start was installed about 8 years ago - no issues with it.

I do know of an issue where the driver's door sensor doesn't turn off the battery, so i always open the passenger side door and it shuts down.

Is the issue cheap walmart batteries, perhaps, or something easily traceable? The truck has had a weird issue for years where the headlights dim a bit (barely noticeable) when driving at highway speeds sometimes, but not sure if that's normal.

I replaced the alt about 8 years ago with a rebuilt Motorcraft. Issue started about 5 years ago.

 

This method may be pretty dated but if you have a multimeter that can measure DC amps, you remove the negative cable while keeping the positive cable on the battery, clip one end of the multimeter leads to the (removed) negative cable, the other end of the meter to the negative terminal of the battery, then select dc amps on the meter (with the meter leads in the correct position). As long as the draw is under 10amp with the switch in the off position you should get a reading of near zero amps normally. If there is a draw (any amo reading above near zero) then you'd systematically remove fuses one by one until the meter reads near zero. That effectively narrows down which system is causing the draw. Just cross reference what fuse that goes to then you can start removing connectors to narrow down exactly which component is causing the draw. It can be super time consuming but the usual suspects are radio and other dash conponents. Id start with those. That is assuming all of the cables have good clean connections and the battery is in good condition of course. If that's not the case the readings will be off. I know i have to clean my cables every year or 2 due to corrosion. That's how we used to do it years ago and I'm not sure of there's a better way now days. You can get a cheap multimeter for under $30 on Amazon I believe.

 

I got my '06 over 4 years ago and it had one of them Walmarts Ever Start batteries in it and it hasn't giving me a single issue.

The only issue I've had was battery draining overnight - in my case I found out it was because I had something plugged in to the rear 12v outlet and I didn't realize it was "always on" (I thought it came on with the key)