Just a little under 4.20v measured by a not cheap but not expensive multimeter. For me, it is not so important to get it exactly when it goes to the third flash, so I don't know how long it has been flashing three flashes. One of my older, less expensive 18650's takes forever to 'top off', and after reading about that feature on the i2 charger here on CPF, I don't sweat it too much. I have compared voltages against my two multimeters and with the voltage readings from my Nitecore TM26 and Nitecore P12. All of them do the job just fine for battery readings: less than .05V difference, I believe. The P12 only measures to the nearest .1V. The two DMM's are never more than .01V different the few times I have compared. Good enough for battery testing for me. Just not sure how 'exacting' you are.