I was given a link to this site in regards to the issue of what battery warning voltage is appropriate when using a single cell LiPo. When using my XG-8, I set my battery warning voltage to be at 3.6V. When the warning goes off, I recharge the battery and typically put in about 80-85% of the rated battery capacity.

I've not done much quantitative testing, just a few quick tests when I first got the radio. My first tests indicated that the telemetry display of the receiver voltage will not go below about 3.2V (or something like that). To me, that suggests that there may be a minimum voltage regulator in the circuitry.

Originally, I used 3.7V for my alarm voltage, but found that I was only putting in ~60% of the battery capacity when recharging. Someday I'll try 3.5V to see how much closer it gets to the edge!

Which receiver have you tested? Look like that yours can work down to 3.6V.
I only tested my RG831B receiver, the telemetry reading just stayed at 3.7V all the time even though the battery voltage dropped below that level.
I really want to know if other pilots have done similar testings to confirm this.