trail-explorer wrote:
You are overthinking it. If the truck starts fine, keep the batteries.
Load test them at an auto parts store. That's going to tell you more than taking voltage readings.
If the starter is sluggish and turns over the engine slow, replace.
Done.
That's the typical regime with starting batteries.
All true, but if way off grid you don't want be stuck so far from a battery store and no wheels to get there anyway.. Campers should have a way out of that.
A. start the truck from the trailer batteries if the truck batteries die.
B. always carry a 10amp (say) portable charger in case your converter dies.
C. have some solar in case you run out of battery
D. take a portable gen in case your installed gen dies and there is no solar due to whatever (trees, overcast)