Helicopters generally need about 100 watts per kg to hover. This can vary by about -20 to +100% depending on the drivetrain, blade airfoil, motor efficiency, headspeed, etc.
So, given the helicopter's weight and cells:
estimated amp draw = (helicopter AUW in grams) / voltage
An ECO 8 AUW is around 1500 grams, and uses 8 cells, so:
estimated amp draw = 1500 / (9.6 * 10) = 15.6 amps
Note: This amperage figure is NOT the maximum required during hovering, only the average figure. For example, if you reduce power while hovering and the helicopter starts descending in its own downwash, then you will need substantially more current to halt the descent because the blades are less efficient in turbulent air. Therefore, you need a battery/ESC combo that can handle about twice the hovering current in order to have a reasonably safety margin for recovering from bad situations.
Note: The 100 watts/kg figure is very dependent on headspeed. This 100 watts/kg figure is reasonable for:
FP wide bladed micros at 1200 rpm of head speed
FP and CP narrrow bladed microhelis at 2000 rpm of head speed
nonmicro helis at 1400 rpm of head speed.
Power consumption is very dependent on motor and headspeed. For example:
ECO 8 w/Mega 16/25/3 @ 1400 rpm: 105 watts/kg
ECO 8 w/Mega 22/20/3 @ 1600 rpm: 174 watts/kg