Lithium Ion (Li-Ion) battery technology is one of the fastest growing trends in the tool community, and certainly for good reason. Lithium Ion batteries have the best energy to weight ratio, meaning they pack the most power with the smallest amount of bulk. They also experience no memory effect or, lazy battery effect. This occurs when a battery can no longer accept a maximum charge for having been repeatedly recharged without being fully used (a common symptom of Nickel Cadmium (NiCad) batteries). Li-Ion batteries, conversely, have absolutely no memory and can continually accept a maximum charge. Additionally, Lithium Ion batteries have a very slow rate of charge loss while the battery is disengaged.
Lithium Ion Batteries What You Need to Know