Will "fast charging" my batteries reduce their life cycle?
Yes, the maximum number of charge cycles that your rechargeable batteries can endure will be somewhat less using fast chargers vs. slow overnight chargers. The cycle life attained is dependent on many factors including the rate of charging and discharging as well as the depth of discharge between charge cycles. In other words if you want to attain the highest number of charge cycles use a slow charger and begin recharging your cells before they are 50% discharged. You would be however, sacrificing the maximum performance and convenience your batteries are capable of and were designed for.
In our opinion it would be worth sacrificing the convenience of fast charging only if the replacement cost of your batteries were significantly higher. If you got only 300 charge cycles instead of 600 charge cycles your cost per charge would still only be 1 penny per charge instead of 1/2 penny per charge. Compare that to the cost of a throw-away alkaline cell of as much as $1 per cell. NiMH cells can supply as much power as hundreds of throw-away alkaline cells. NiMH cells cost much less to operate regardless of the ultimate number of charge cycles attained.