What comes to light use towards the end of the battery, at least in my case it is required, because if I load the phone too much when the battery is almost empty (over 200mA current, WLAN, GPS, Screen up, etc.) the device shuts down before the bq27200.sh 5 reports the EDV1 bit changing from 0 to 1, which is required for calibration.

The battery voltage has to remain between 3248mV and 3198mV for 15secs for the EDV1 bit change to 1, and if it drops below 3198mV too quickly, the device shuts down before correct calibration. This info from Estels guide.

Edit: It's around 3300mV that the drop becomes fast, so at that point I shut down the gps and screen. Wlan was changed to GPRS at 3350mV, because GPRS connection at start draws a lot (600mA) so it could empty the battery too quickly if done too late. Of course change to offline mode could be done later.