I just got a new battery in December last year. From time to time I was "thinking" I was charging the battery from the jumper posts in the engine bay since I didn't invest in a Ctek. Well the battery only made it until the beginning of November and needed to be replaced. It only ran me $7 to swap at Costco but I would have to assume then that the posts do now allow the battery to charge? And maybe now it is time to invest in a Ctek.

 

I have been doing this for 6 years with no issue. However I do use a CTEK.

 

I wonder if by change I am not using my charger correctly then. I thought I have been doing it properly and it never seems to take a charge. My booster/charger always shows 100% like it isn't needing to take a charge.

 

Almost ditto.
I have been maintaining my battery (the original) via the engine bay charging posts for over eight years now and it is still going strong.
Not a CTEK, a different 15 amp 7 stage tender/charger.
About five years ago I hard wired the connections to the charging posts so I simply have to plug the pigtail in, takes 10 seconds flat to connect, I have a thread with pics around here somewhere.

 

As above, perfectly ok to charge from the posts. I wonder however if your battery "died" so early in it's life because of the dreaded OB11 issue? If it was constantly draining it would explain some of your issues.

 

I bought the Ctek and used the accompanying eyelets to semi-permanently install it to the main AGM battery, as recommended by my JLR tech. As mentioned, there are several threads about connecting tender/chargers to the AGM.

 

Ditto.