Buick 2001 Century Owner's Manual page 86

2-16
To replace the battery:
1. Insert a flat object like a dime into the slot on the
back of the transmitter. Gently pry apart the front
and back.
2. Remove the old battery and replace it with the new
one. (Use type CR2032 or an equivalent.) Make sure
the positive (+) side of the battery is facing down.
Do not use a metal object to remove the old battery.
3. Snap the top and bottom together, making sure the
halves are together tightly so water won't get in.
4. Test the operation of the transmitter with your vehicle.