A new method for determining plasma parameters from beam current transients resulting from short pulse 1+ injection of metal ions into a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS) has been developed. The proposed method relies on few assumptions, and yields local values for the ionisation times 1/ne^inzq → q+1, charge exchange times 1/n0^cxq → q-1, the ion confinement times τq, as well as estimates for the minimum plasma energy contents ne < Ee > and the plasma triple products ne < Ee > τq. The method is based on fitting the current balance equation on the extracted beam currents of high charge state ions, and using the fitting coefficients to determine the postdictions for the plasma parameters via an optimisation routine. The method has been applied for the charge breeding of injected K+ ions in helium plasma. It is shown that the confinement times of Kq+ charge states range from 2.6+0.8-0.4 ms to 16.4+18.3-6.8 ms increasing with the charge state. The ionisation and charge exchange times for the high charge state ions are 2.6+0.5-0.5 ms-12.6+2.6-3.2 ms and 3.7+5.0-1.6 ms-357.7+406.7-242.4 ms, respectively. The plasma energy content is found to be 2.5+4.3-1.8 × 1015 eV/cm3.