The 30 + min quick charge SHOULD give the same durration of flight (+/- about 5%... not just 10% to 20% of the same for sure) as the slow charge. There's definitely something wrong somewhere....

Double-check the settings of the charger, to be sure its set for the correct number of cells (assuming it has that as a switch setting.) Make sure its set for the correct type of cells. (If its set for NiMh and you're charging NiCd... it'll quit early... again assuming it has the switch setting, and not an autodetect.)

You can verify if the charger is working correctly by charging/cycling another battery... such as the 4 cell RX pack, or a second 6-7 cell flight pack in both modes and verifying that you get close to the same capacity with both types of charge.

I don't know if your charger has cycling capability.... it would be helpful for this determination. Testing with a different battery will prove if its a charger problem or a battery problem. (likelyhood of getting 2 bad packs from 2 seperate purchases out of a store that sell a lot of them is near 0... packs that sat on the shelf for 1 or 2 years have a higher chance of being bad.)