Lithium batteries, (LiPO or Li-Ion), are high-discharge batteries designed to be used with upgraded or high-end airsoft guns to drastically increase performance. Because Lithium batteries can discharge at a much faster rate a noticeable reduction from the time you pull the trigger to when a BB is actually fire (called trigger response) is observed. Lithium batteries also give the operator the choice to increase the voltage from the typical 9.6v NiMH batteries to an 11.1v LiPO battery and thus increasing rate of fire. While not all guns are capable of handling the power of a 11.1v battery, many are able to be upgraded by the Airsoft Station professional airsoft gunsmithing department to handle the stresses of using these batteries!
Additionally, Lithium batteries require a special balance charger to properly charge. Always store LiPO batteries in a safe and cool place and never charge them unattended.