LiPo Balancer
The LiPo balancer cell acts like a big and very accurate zener diode; when the cell voltage is under a threshold fixed by the user the system is in “idle state” and watch only for the voltage with a equivalent resistance of some KOhm and a negligible current shunt. When the voltage reaches the threshold the balancer element will start to shunt current from the cell with an internal power resistor.
   LiPo Balancer
For more detail LiPo Balancer website
www.seven-segments.com