You just need a switching power supply so the voltage applied is about 14 volts (one 12 volt battery). I have used a $20 unit that accepts up to 40 volt input and has an adjustable output voltage.
I need an intellegent charger circuit which charges the battery according to battery charging algorithm.. In first phase, battery should be charged in constant current mode, then in constant voltage mode and third in trickle charging more. Just using a switching power supply will not help.