The manual states to change them every 12 months. Trust me on this do it now, then change them on an 8 month schedule because once that fob battery goes dead it gets really annoying having to enter your override code (you did program one right?) to start the bike and even then the alarm system can act funky.
Yes I had BOTH fobs die within the first 8 months, went to start the thing, alarm starts blaring -- enter the dang code -- after pulling out the wallet card with the directions -- finally the alarm shuts off, bike starts, casual observers are wondering what my problem is, some laughing, some scowling - heck I was wondering what my problem was it took me so long to get the bike going -- So now I'm keeping fresh batteries in the tourpack (I figure on buying an extra pair every time I change them) and then I can change them at the first sign of trouble.