Centre pin is detect to laptop where you connect is original Dell laptop or not,when detect only Dell brand,continue to charge immediately,there in 0 voltage on centre pin,in the circuit centre pin lead connect to a small transistor centre pin soldered on the board to this left or right pin of this transistor ,and left&right pins are running on 0 volts both side to sense the Dell original laptop battery,in case of out of order to charging the battery you can use to sense another pin of transister to solder the centre pin lead after doing this your centre pin sense the laptop dell ,tricky way to use charger for hole life,tip: any one pin of transistor can be use for sense the laptop dell brand battery