Locate the slot on the side of the keyfob. Insert a flat screwdriver and twist it to separate the key housing.
Remove the housing from inside the key shell. You will see the battery housing that you need to open up.
Use a screwdriver to pop out the back cover. You will need to push inside all the 5 tabs. They just need to be pushed in slightly to allow the black plastic to release.
Remove the back cover. Slide out the old battery. Install new CR2025 3 volt lithium battery.
Install the battery shell in reverse order. If the buttons of this remote are worn out you can replace the buttons while you are at it or even the whole case. A new shell for this remote can be purchased on Amazon, click here to see new shells for this Toyota remote.