We have a HS 250H, 2011 model.

The car dead last night and i jumped start her.... I am just wondering where is the 12 volts battery located in the car? i am looking toward to replace it.

thanks a lot

 

The 12 volts battery is located in the back (behind the back seat) - there is little opening in the trunk you have to remove the carpet cover to be able see the latch and you will see the battery

 

Just be aware it's not a typical lead-acid battery, as it's exposed to the car interior. It's a gel battery, and likely hard to find outside a Lexus / Toyota dealer. It's also about $250.

 

is that possible to upsize the 12v battery?

 

No, you are limited in space and in type of battery. This is really a dealer only item unless you make modifications to the mounting system as someone has posted here a long time ago. Considering that this is the only time you will have to replace the 12 volt battery as they last 10 years, just bit the bullet and get one from a Toyota or Lexus dealer.