Let me know if you got a circuit for that.
The trouble with resistors is that you will not get a constant 30Amp. Given...
v=ir, v=7.2, i=30amp, r will need to be 0.24ohm.
and you will dissipate 216watt.
But you will also noticed that when a battery pack is discharging, the voltage will not be constant. So, you need a constant current regular. But, with so much power go to waste, it might make sense to discharge the power to charge, maybe an lead-acid cell.
So, constant current 30amp regulator to a step-up DC voltage, and to a lead-acid charger.