I've just bought a 2 cell 7.2v 1400mah lithium ion battery for my Aerohawk but it doesn't lift the heli off the ground[]

Midland Helicopters state that it is suitable for the Fixed pitch Piccolo so I took a chance thinking the Aerohawk is a similar size but it didn't pay off.

Is the Piccolo a much lighter heli or is there something else I need to do to use li-ion baterries? Do I need the 3-cell 10.8v (don't want to cook the board) or is there a suitable upgrade battery anyone can suggest?

It flies well on the stock batteries but I want longer than the 6-7 mins flight I'm currently getting.

I use a Ripmax Mercury EX charger that has 7.2v 2 cell 1400mah setting so I dont think its a charging problem.

Any info appreciated [8D]