Replaced my 12V battery

Went out to start my 2012 v after sitting overnight. It unlocked, and the door open light illuminated, but the car would not crank. On/off button would only cycle between off and orange. I measured the voltage of the 12v battery and found it at 9.6v. I disconnected it from the car and charged it up with a battery charger, but it dropped back down below 12v within a couple hours. This was my original battery from 2012! Have never had a 12v battery last anywhere near that long in a car before! I purchased a new battery from the Toyota dealer. It was actually cheaper than the Advance Auto version - $200.04 out the door. And an 84 month warranty! I wonder where this car will be in 84 months...