Only 1 guy suggested that it may not jump start the truck. And he may be right since the OP likely has a diesel since he said batteries, plural.
However the OP is preparing for another bad alternator. In which case a jump start would not help him at all. And the equalization of 1 - 200ah battery into 2 ea 100+ ah lead acid batteries wouldn’t get him far unless it is a 30 year old mechanical injection diesel and he can drive with no other or few things using any power.
There’s a whole bunch of hokey riggin including a jump start that “may” get him down the road a little ways, but none of that matters if one is “preparing” to handle that issue.
Fck, just pack a spare alternator and a jump pack or cables or both. No need to get fancy. Just bring the part you’re worried will break. And if you’re not totally unobservant you’ll see when it quits before you use up much of the battery reserve.
The weird tangents that get explored or entertained on this forum are quite often completely baffling….
