High discharge rates heat the battery, and can give a "false" low voltage reading due to the heated cell having a higher internal resistance than a cool cell. thus, the bateries could read at .8 v per cell and still havemore retaned energy than if they'd been discharged more slowly.

If the packs are discharging overnight in the plane, even though the switch is off... there's a problem with the switch or the wiring of the system. (maybe the switch is cutting off the power from the motor, but not from the RX... Where in the crcuit is the switch? between ESC and motor of between battery and ESC?)

BTW: The high charge rate you are normally using could alo be a be a problem... an is the most likely case for you to consistently get the 720 to 440 mah capacity from your 800 mah cells. It may give a slightly higher capacity just by charging at appx 800 mah (at home before going to field, charg at low rate, at field use the field charging high rate.)