Phantom2 Vision+ losing power with batteries at 75% strength

[pilotodroneo]

I have two batteries purchased at separate places with only about 12 charges on them. Yet, when the battery strength is between 70 and 80%, the quadcopter loses power and gets erratic and I can't seem to get it to rise up in altitude. I can barely maintain control to land the thing. and go through broken blades like a hot knife through butter! I am getting no abnormal battery warnings. The diagnostics look normal with all cells appearing normal at 3933. currrent is -915mA. voltage says 11792 when it's on and sitting on my desk. serial number of one of the batteries is 1341. I'm having a lot of problems with the phantom just dropping out of the sky at this battery strength as well. Seems to fly nice at 100%. I remember when I first got the unit, with older batteries, I could go down to 20% and it will still fly up. Any ideas? I'm losing confidence in this machine. I have overwritten the firmware several times. Re-calibrated until I'm blue in the face. Calibrated the compasses each time and it says "ready to fly." thanks!