This method can be used when the source is non-regulated.It is usually implemented with a transformer with a high output voltage comparing to the battery voltage.A resistance should be used to limit the current flowing to the battery.A diode can also be used to ensure unidirectional power flow to the battery.In this method the current starts at full rating and gradually decreases as the cell gets charged.This technique is only applicable to Sealed Lead-Acid（SLA）batteries.