Correct charging voltage

I charge using a Mastech HY5020E power supply, not a dedicated charger. It has adjustable voltage and current. My question is this, what should I use as the "chrarge to voltage" per cell. If the answer was/is 3.3, then Id set my voltage to 6.6 for a 2s pack. What I have been doing is seting voltage at 3.7v or 7.4 for a 2s. Id like to know what it should be per cell. Also since Im here what can I expect my voltage drop to be under load. I will be using a 10s set up on a Tango 10-08 (800KV) motor. Just to put some numbers out, say a 10S pack charged at 3.5 volts per cell, would equal 35 charged volts. whats my voltage under load gonna be? and how fast is that drop seen in the system?

Correct charge voltave is 3.6V per cell.
Don't forget to use a diode to avoid pack to discharge in the Mastech.
Better to have a wattmeter after the diode to check process.