Is simpler than that, a coil and a a capacitor, and a transformer for 10khz few turns on the primary and 3 times more on the secondary with 3,5mm wire. Connect everything, secondary, choke, capacitor, cells and than close again in the secondary what you get is a parallel resonance, use a capacitor between primary leads and a capacitor from source to drain of our mosfet, Use a diode in series from positive side of the batery to the primary... Resonance simply . connect an Ameter in series with the circuit and on the primary. and a voltmeter and frequency meter between the choke sides.