The car is 2014 Sienna. I may have understated the age by a lot when I said the battery was ~5 years old. I could faintly make out the word "Toyota" on it, so it could have been the OEM battery!
I did a day trip with total drive time of ~5 hours and the next day the battery still tested at 12.2v. I've since replaced it with an Interstate battery from Costco for the cheap. Going forward I will need to drive the car more frequently and for longer. I have another car and only use this vehicle to commute 10 minutes to the train station once a week, plus other odd trips here and there.
