Re: 2011 sienna dead battery
I have a 2011 Sienna driven 7000 miles in 14 months. I have had dead battery issues about 5 times. I keep it in a garage and drive about 4 to 6 days a week. After a few months it wouldn't start. Assuming it was my fault, I charged the battery and it was good for a few more months. The next time it would not start I called my dealer. They said the battery was bad and replaced it. The same thing happened during the next 6 months. The dealer also tested for an electrical drain for 1 day, and replaced the second battery. So, 2 months after that it doesn't start. I drove Monday, Tuesday, Wednesday, not Thursday and it's dead Friday morning! So back to the battery charger all weekend. My service guy (as helpful as can be) provides a loaner car and checks battery, charging, and runs the electrical drain for 2 days. Their conclusion: everything is fine, I just don't use it enough.
update: April 2013
I still notice my starter slowing at cold starting about once a month. So I hook up the battery charger. After 2 1/2 years I finally heard the infamous "humming" noise coming from underneath while it was parked in the garage at night (I've read it has to do with the gas vapor control system.) Some say these newer electronic demands wear down a battery. Anyway, I still check with the Toyota dealer occasionally for any new data regarding this battery issue, I always get a quick "no."
It's interesting though...I also have a 2008 Avalon, with a similar power plant, and it's original battery has never failed to start, even parked for 5 weeks during a vacation!!! It is driven about as much as our Sienna.