LiPos do not like to be "undervolted."

A battery is a voltage AND a current source, so the amount of capacity left is proportional to its voltage as the charge is being emptied out of it...

If you're going to run LiPos, make sure your ESC has a cut-off feature and that you set it correctly, depending on what configuration the battery (2S?, 3S? 4S?).

If it doesn't have one, you can get some piggy-back systems that will do an alarm or cut-off for you... Again, make sure you set it correctly with a bit of margin...