That's 2 of 3 components to this though...
If the Batteries are all they should be and the Alternator is doing its job, then you have sufficient reserve power and it gets replenished as it should. So, all that's left is that you have a Drain. All the power that batteries have is being siphoned-off by something as the truck sits. It's called a Parasitic Draw
and you have a puzzle to solve
For this there is the Scientific Method
, if you have the tools & understanding you do it this way ->
In that vid he talks about a 50mA max and how some vehicles require 1/2hr to settle-down after the last thing gets activated. Our trucks can take that long, and actually draw a little more than 50mA when finally ay rest.
The next way is a Caveman Method
if you don't have those tools and just a simple "process of elimination". If you know the batteries go way down overnight, just take 1/2 the fuses out and see if it happens again.
If not, take Half of the Other half.
If so, put only 1/2 of them back.
Do this everyday, over & over, until you limit it down to the Single fuse that will stop it from happening. Then you can start to unplug stuff associated with that circuit (it's usually something like the Radio / Cluster / something like that) and check the wires that go to them...
It's a project and a puzzle