Update.. the dealer told me that the battery is depth dead and they charge it and now its okay. But l told them that l try to fully charge the battery too but still dead in the morning. And they said l need to drive my car atleast 45 minutes everyday to get the battery charged, sounds ridiculous. I drive my car to and from work and pick up my kids which is 5-20 minute max. I got other vehicle standby for 2 weeks but turns on everytime l wanna use...
We got 8 months with 8000k, same problem. The dealer said battery is dead and they charged it and its ready to roll but l told them that l charged it fully through and still dead then now They want us to drive our van 45 minutes atleast everyday to keep battery full which sounds ridiculous coz l only use the car to work and home wchich 20 minutes max.
Unless your running a bunch of electronics in the van your dealer is clueless. Unlike a regular ICE vehicle driving a high amperage starter motor, the Sienna 12v battery has very low drain only powering up the computer and energizing the HVB relays, and will recharge to full very quickly.
Your battery is toast (internally shorted) if it's not holding a charge OR there is a phantom drain. I had this on a truck many years ago. Battery would be dead every morning. Only way I found it was one night I noticed a glow under the front end. Turns out the gravity switch for the hood light was stuck in the "on" position. Removed the bulb, no more drain, problem solved.
I would start with anything added after-market, look for anything you (or kids/spouse) leaves plugged in, check that the far rear light above the tailgate door is not turned on, etc. It may take some trial and error pulling fuses (using an amp meter if you have one) and testing to see where the drain is.