I briefly saw a "service battery charging system" warning on the cluster a couple days ago that went away after a few seconds. I realized I had left my lights on for a few minutes after powering down the car and it made me immediately suspicous my 12V battery was dying. I measured the resting voltage at 11.7V (multimeter across the terminals), obviously below nominal.
Much to my surprise the battery was the original Delco battery. Sticker said 01/14 -- so 9 years old!
So, the purpose of this post is as follows.
1 - If you haven't checked your +12V battery, it's probably time to do it! All you need is a cheap multimeter. Lift up the cargo cover in the back and you can access the terminals, no disassembly required.
2 - I've never had a car battery last anywhere near 9 years, so I would definitely recommend the ACDelco AGM battery which is what came with the car. Part number is different but otherwise appears very close (ACDelco EVLN2AGM). Rockauto has them for $135 plus core, plus shipping, plus tax. Out the door for me was $165.