I just checked my logged on battery replacements on the Monte Carlo.

2002 - Monte was new.
Oct 2005 - Replaced battery - 60k miles.
Sept 2009 - Replaced battery - 120k miles - w/Sears Diehard Gold
Sept 2012 - Battery needs to be replaced - 171k miles.

- Mark
  
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 * Origin:  http://www.weather-station.org * Bel Air, MD -USA (1:261/1304.0)