You say chargers, alternators, etc. “all seem to be functioning”. Learn your system in detail and check that your charging profiles are set correctly and working correctly. It’s worth the effort because incorrect charging is one of the most common ways to kill your batteries.
Lots of new batteries are damaged or killed because they are installed to “fix” the problem, when the charging system was always the cause. I always suggest that you test your charging system and make changes and adjustments, including testing, with your old batteries in place. Then put new batts into a system that you know works. That way you don’t abuse new batts while you are sorting it out.