Any proof or reason for "shorter life" under load?
OK, so charging a dead battery is more "work" for the alternator, but why should that shorten its life? The construction, conductors, and internal parts are sized for the current. Is the "shortened life" based on something real, or is it a myth?
I could see that an overload would damage something in the windings or in the regulator, but other than that, I don't know of any basis for a claim of shorter life for the alternator.
High-rate charging of the battery is another story, though - you need to look at the charge rate requirements for the particular type and brand of battery you have. Keeping charging cable size down could actually help limit the current - you might not want to use #4 cable. You would want to use a disconnect or a battery isolator, or you'll end up with two dead batteries.