i didn't understand your capacitor method so i can not say.
but i have built an incredibly efficient battery charger using the "open an inductor" method. yes a free wheeling diode is used to provide a path to send the voltage spike to the charge battery. so i thought i would mention it as one way to get a high voltage in very short period of time.
my application .. its a two battery system, one 12V battery is used to charge the inductor, transistor open circuits the inductor, 1000V voltage spike goes to other 12V batter via a diode.. it is pretty different method to charge a battery .. it is not a constant current method, it is pulsed voltage. i know putting 1000V spike on a 12V car battery sounds like an explosion ready to happen.. but the timing is so short. like passing your hand through a flame .. if you're fast you do not get burned. nice thing about this method is it simultaneously breaks down any plate build up that occurs during use so it is like you always have a brand new battery .. not one that can only be recharged X number of times. also.. there is no heat build up (which is the true killer of batteries) since we are not using constant current but rather spike of voltage.