If you want to learn all about maintaining and getting the most out of your battery read this....
In between all the rants is a lot of good information.
Normal life for a battery should be 6-8 years if properly maintained. Undercharging or overdischarging will shorten life and capacity fairly quickly. And I would guess most people do both. I certainly did when I started out.
Your tow vehicle will take hours to fully charge a battery. I have noted on one 3 hour trip that we got about 10Ah back into the battery during the trip home. This was on a battery around 90% charge and the last 10% is the hardest to get back in the battery and takes the longest, but it is also the most important.
Same goes for the trailer converter. It can take days being plugged in to fully
charge the battery. They drop into float (~13.2volts) after a set voltage or predetermined time too early and don't get a full charge back into the battery. They are really designed to maintain a battery while being plugged in not to efficiently charge one.