Battery charger upgrade and purpose of solinoid

Indeed, the truck probably has a monster alternator. The question is how do I get that power to my AGMs to charge more efficiently?

Also, can I run the fridge on battery while driving? Or will that put too much strain on the alternator?

Finally, how can I upgrade the battery charger when I plug into AC so that is faster and more efficient as well?

And, yes I do unplug the 7 pin when parked for extended periods of time.