Probably a CR1616. Open it up and see what battery it takes.
CR1616
3 button fob 2003 onwards cr1616
Lithium CR1632 (2008). I just replaced mine and got it from the dealer.
CR1616
A small battery that fits in a key fob or remote.
Open the key fob, remove the battery and look and see what size it is.
Open it up and check and see.
change battery in a 2007 toyota avalion key fob
Panasonic CR 1616
remove plastic cover next to driver door handle using the key in remote fob and then insert key into lock.
Yes, there is. On my 2007 ES 350, it's a CR1632 button cell. I had a little trouble finding one locally when mine died. Even the Lexus dealer didn't have it! But I finally did find one at a larger Radio Shack store. Just remove the metal key from the fob, insert it into the slot exposed near where the key went, and pop the fob open. Insert the battery, and you should be all set.
CR2450