Manufacturers recommend charging batteries at the rated capacity i.e., a 500 mAh battery should be charged for one hour at 500 mAh.  The exception to this is the batteries with the letter "R" at the end of the designation (500AR, or 2000SCR).  The "R" means rapid charge and discharge.  "R" cells are either very expensive or not available.  Hobbyists are notorious battery abusers.  Batteries that are not designed to rapid charge are routinely over charged by charging and discharging them too fast.  NiCad cells have a finite number of cycles. 

Abuse will decrease the number of cycles.  Electric flight hobbyists are willing to accept the shortened life of the batteries for performance. There are ways to cut these losses.  Don't charge at a rate more than twice the designated capacity of the battery.  Don't charge a hot battery.  Get enough batteries to fly one, cool one, and charge one.  A way to speed up the cycle is to make a 12 volt field battery cooler.  Tape a 12 dcv muffin fan to a 6 inch length of 2 inch PVC plumbing pipe.  The muffin fan is available at Radio Shack for cheap or find an old computer power supply fan.

Discharging the battery at the rate of 10 to 15 amps is the other way electric flight hobbyists abuse batteries.  These high discharge rates produce heat.  Again there are ways to cut your losses.  Airflow over the battery during flight will help.  Vent holes in the cowling is a good idea.  But more important is the throttle settings during the flight.  Full bore for the entire flight is definitely too hot.  Try some throttle off time and some half throttle time.  This will extend the flight time and battery life.