I have one also, Had my first one implanted in 1991. On my fifth one right now and I get on average four years per battery.
Yes in August 2009 I had a pacemaker/ICD implanted - my model is a Boston Scientific Teligen 100 - extremely small and great battery life - I'm at 8.5 years as of right now.
Mine was implanted due to malignant arrhythmia's called polymorphic ventricular tachycardia.