I have heard of car batteries lasting 10 years - but I would consider that an exception. somewhere between 5 and 8 years is a good time to proactively replace.
then again - sometimes - depending on year round weather conditions and milage - you can have other items such as a fusible link or an alternator go bad - and it may appear that the battery has died - when in fact something else in the charging system is really the problem.
'09 RL Ruby Red Manual
3rd brake pulser-seq'l tail lights
Retracting motorized front license
HID low beam & fogs
DDM Works - Charge Tubes,Cross Bay Brace,Tunnel Brace,Center Console,Fender Trim,Sway bars,Drilled Rotors,Hawk pads