Jeep issues

I have a 2019 Jeep compass that I’ve bought recently. The aux battery was dead when I first got it. It was replaced and died again so I left it alone. It’s annoying anyway. Since owning the Jeep, it would charge at 13-13.7 volts while driving. Fluctuating but steady. I decided to change the battery out of fear of it dying. I did so, and ever since, I’ve had to jump start my Jeep daily. I replaced the aux battery, same issue. Replaced the main battery twice. Same issue. Idk what to do. I unplugged the negative terminal once and it died, but it hasn’t done that since and I’ve unhooked the negative terminal a few times since just to be sure it’s not the alternator.