I had to replace the fob battery on my '09 bike after less than 2 years. They are not expensive, about $ 6.50 for two batteries from K-Mart or Walmart. The worst part was trying to open the fob without damaging it. Be patient and do not force it. Try finding a screwdriver with a blade tip that perfectly fits the slot provided, or modify an old screwdriver by grinding the tip to fit the slot. If you use an improperly fitting tip, it will gouge the plastic as you try to twist the screwdriver to pry the case open. These fobs are very hard to open without damaging them. All least mine were.
Actually, you could have the dealer replace the batteries under warranty, but for $ 6.50 it is not worth the trip, and I bet they do not stock these batteries.