This circuit be lead acid battery charger again interesting circuit, Because it can charger get both of 12V sizes and 6V. By change with switch only and this circuit charging with current about 1Amp. When see the circuit you will think us uses integrated number highly popular circuit be LM317K again. By when you Close SW1 make can charger battery 6V get. Which have voltage come out about 7 Volt. But enough Open SW1 as a result use charging battery 12 V get. Which give volt come out about 14Volt supposing that you use battery 6V 10Ah take time charging current 10 long ago hour. The diode D3 and D4 help protect voltage turn back from battery get. The detail is other see in the circuit.