Rrabenold

I am having a problem with my 2015 1500 Silverado LTZ, 46,000 miles. The problem is hit or miss though. It almost seems like my alternator is not charging my battery. My battery gauge is dropping down close to 9 and every now and then I get a "Service battery charger" or "battery charger active" message on my dash. The first time this happened was when I used my remote start although I dont know how that could effect it because I always use the remote start and I have had the truck since March 2018. The first time I had this issue, I needed a jump start and then I was good for 4-5 days. Now its happening again and I am getting the "battery charger active" message while the battery gauge is almost to 9.

I had my battery, alternator, starter tested and it all checked out great so they wont replace anything. I find that odd but I am no car/mechanic guru. It seems to be struggling to start up as well when I am getting these warning messages.

Any ideas? Fuse? Entire electrical system issue?
Note: I only have two cords plugged into my outlets to charge phone and headphones.

Appreciate the help in advance. -RR