Jeep Grand Cherokee battery?

[sonata]

I have a 2005 Jeep Grand Cherokee and replaced it's battery last year at roughly 38,000 mles (maybe less). The other day (15 mos later) I came home from a 2 week trip and my Jeep was dead... nothing worked, not the alarm, not the door locks, not the clock. I got a jump start and it seemed to work fine. A few days later I took it to the dealership for an oil change where I told them of the problem and asked them to check battery... they said all was ok. 3 days after that I got into the car and tried to start it only to find a dead battery again but at least this time it "clicked" rather than being flat dead. I got another jump start and went to Jeep and told them... today I have a new Mopar battery without charge cause the old one was still under warranty. I'm glad I didn't have to pay for the new battery BUT why did I need a new one in the first place after only 15 mos? Is it time to put my Jeep to bed forever? (it only has 46,000 miles) I don't want to spend money on another car but I also don't want to be nicked and dimed to death, plus the inconvenience of a car in the shop is, well... inconvenient(!) Advice please... I'm all ears. Oh, is Mopar an inferior quality battery? Is Interstate or EverReady better?