I would like to assemble a 12v DC-DC voltage regulator to charge a few 12v lead acid batteries laying around. I have come across this circuit (here is the link, Lead Acid Battery Charger Circuit Diagram and Its Working ,but I have also added a picture) ,but I unfortunately do not have any BC547 transistors. I have been told that the main difference between all transistors is their impedance in ohms and voltage limit between the gate drain and source. What I am asking is if there is any simple way to determine if a un-recommended transistor (or mosfet, etc. and or could this apply to any ic as well?) model will work in a circuit based off of a few comparisons between the recommended and un-recommend part schematics and if a generic 2222 transistor will work for this circuit.