charger with constant current

Hello,

I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.

Is this a question of timing, or should I approach the problem in a
totally different way.?

ken