You will know that you have as close to resonance as you can get when you feed the coil/cell series combination with a sine wave, then from a low frequency adjust the frequency upward, you'll see the voltage across the series coil gradually increases till it's equal to the voltage across the cell (which is dropping).
To do this you may need to float the circuit (with no earth) and place the CRO earth clips both at the coil to cell junction point. Use dual trace chopped mode. The first probe goes to the feed point at the top of the coil and the second probe to the bottom of the cell.
When the peak to peak volts across the cell on one channel equal the peak to peak volts for the coil on the other you have resonance.
If the cell is not being driven into conduction by the generator the phase difference between these two equal voltages should be 180 degrees at resonance. If the cell is conducting the phase angle will be reduced and the voltage will also change affecting the measurement.