We are using this part on our micro bots to charge the lithium battery.  Lithium batteries require a constant voltage when you charge them if the voltage is to high or too low, they can (will) fail catastrophically.  This part is able to transfer a constant voltage to the battery to charge it, after the battery reaches maximum capacity the voltage is cut to 1/10 which is know as a "trickle charge" this feature will preserve battery life and allow the micro bot to be plugged in for an extended time and not suffer damage to it's components.