Leaving them stored fully charged can lead to a puffed pack as well... My dad bought some 5000mah 2s for his planes, charged them and never used them even once. Maybe 3-4months. Now they all have puffed cells.
Well he learned the hard way... But I have left packs charged for maybe a week or two and no problems.
Maxx - FLM, MMM, CD Med.36x706s
Raja - FLM Ext. MM, 1512, 4s
SC8ight - MMM, 1520, 6s
D8T - MMM 1717 6s