Heres a link to some good information on batteries: http://www.toolcritic.com/battery-power.html For myself, I am a practical man. I leave the batteries in the charger and in the tools. When they are low, I charge them. When they are old, I replace them. They are expensive, but life is short and my time is worth more. Don't let your batteries get too hot and don't run them too low. My partner, who wrote the article above, keeps a timer on his charger so that it shuts off power to the charger when the battery is charged. It's probably a good idea.