I have a 30 min Duracell charger as well. It has not destroyed any batteries yet. I am still using 700 mah and 750 mah batteries because they are still good! I am gonna get some 900 mah batteries today.
The metal contact points on the charger turned green after a while and the lights on the charger blinked as if the batteries were bad. I cleaned them up with my drummel and now it is as good as new.