Odd 12VDC issue - is it the charger or battery or both?

The PD converter in our camper has been great. In over 5 years each on two different Interstate batteries I never so much as added a drop of water. Granted this is with only several few-day trips per year and never deeply draining the battery. It's plugged in 24/7 when not camping. The first battery died (at ~5 years old) because the GFCI had tripped and the camper was without power for as much as a couple of months. The replacement is over 5 years old with no water loss.