If your keyless entry 'fob' still doesn't work after replacing the battery, it might just be a problem with worn out contacts inside the device.  These contacts are rubber-like, yet coated with an electricity conducting film that can wear off with use.
A typical keyless entry 'clicker' for your car looks like mine. 
By using metallic tape and a hole punch, you can fix it....and the fix works g-r-e-a-t !
Tools needed:
metallic tape or (aluminum foil, for which you'll need a tiny amount of glue to make the dots adhere)
hole punch
a little  bit of manual dexterity

Disassemble the device as shown in the pictures.
Using the hole punch, cut out a "dot" of the metallic tape to place over the worn-out contacts inside the 'fob'.
If you cut the dots from aluminum foil, you might want to use tweezers to put the dots in place. I found through trial and error that super glue does NOT work for very long. I happened to have the roll of what I call 'muffler tape' (that's what it looks like to me and I don't rememnber where I bought it, or for what purpose originally)
I just had to repair mine again today after about 9 to 12 months of service. Beats the price they want at the dealer for a new one.
The pictures should tell the story. Good luck.