Service Battery error in Mac OS X

I've had my venerable MacBook Pro since 2006 and as such I've gone through several batteries. Up until yesterday this three month old unit could hold several hours of charge even with the screen at a reasonable brightness and WiFi enabled, but all of a sudden I can't get more than an hour and OS X is reporting the unit needs servicing.

Three questions: How could this have happened? Do Apple batteries have warranties you reckon? Is the Bird still The Word?