Here is the full story. Two weeks ago, I took the truck, 2009 Silverado Crew Cab 4x4, when i went fishing. Truck started and ran fine all day. At the end of the day, I drove it down to my friends house which is about 200 yards from my house. When we went to leave that night, the truck was dead, would not start. In the morning, went down, jumped it, and drove it home. The next day, we took it to AutoZone, they checked it and said it was good. They put a load on it and I came back later and they said it checks out as good as a brand new battery (the battery is 8 months old). So, I thought maybe I left something on in the truck. Took the battery home, started the truck, checked everything in the truck to make sure nothing was on, and left it at that. The next day, I checked the voltage to see if the alternator was working correctly, negative lead to the battery, positive to the alternator and it was showing over 15v. I assumed that is correct. Last week, I drove the truck several times and it worked perfectly. However, on Sunday, we went to go get groceries and I noticed about half way there that the battery gauge was well below the 14V mark. I guess the gauge was on about 12 or 13. As we got closer to home, it was down to about 10 or 11. I set there before turning it off and checked to make sure everything was off and then turned it off. I figured it would not start and just left it. Yesterday, I went out to jump it, tried starting it first, and it started right up with no hesitation. Can someone tell me what could possibly have caused all of this? I am at a loss and not really wanting to drive it. The truck is out of warranty, but only has around 54k miles on it. Again, the battery is 8 months old, and have had no battery issues before this.