This tutorial should work on all key fob models for 2006-2013 model Lexus IS, LS, GS and ES. You will need a small flathead screwdriver and the replacement battery.
Take the physical key stored in the key fob out by pushing the little notch at its end
Use the key on the small gap to pry the fob casing and open split it in half according to the video bellow
Remove the small circuit board
Use the screwdriver to remove the battery
Put the new battery in the socket and reassemble the key fob.
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