Battery or Other Issue???

I went to the lake yesterday with some friends. Got to the lake, parked the truck, and went out for the day (was not hauling the boat). Loaded the boat on my friends trailer, then drove my truck over to help clean/strap down etc. and turned it off. After we were all done and ready to head out my truck wouldn't start at all. It went from turning on like normal to absolutely no power. Friend jumped my truck to get it going. Proceeded to drive the 45 miles home. Things i noticed on the driver home were: down shifting (higher rpm) cause the dash lights to come on and the speedometer to bounce, but maintained truck power, slight flickering of the display lights behind the gauges. As soon as i got home i turned off the truck and tried to start to see if the battery would be up for it. No power. I'm assuming i have a dead battery. it was +/- 100 degrees at the lake, and i'm pretty sure its the original batter (2011 tacoma). there wasn't any corrosion on the terminals. Any advice/help is appreciated.

 

First thing I would check is the terminals. Clean them and see what happens.