I need lipo battery for out-runner Brushless motor (2450KV) with ESC of 12A.
any one please tell about the type of battery.

The LiPO battery have mainly 3 specification.
1. Voltage or no of series cells like 2S, 3S.
2. mAh Capacity like 1000mAh, 2200maH etc.
3. Safe maximum discharge current rating (Expressed in C  Capacity).

C Capacity means the cell can be discharged safely withen 1/C hour.

So,
a 1000 mAH ,3S, 20C battery means,
1. Battery have 3 cell in series.
2. Cell Capacity is 1000mAH.
3. Discharge Capacity = 1000 x 20 mA = 20A.

NOw, in Electrical system,
  Load is the king.
So, if the motor demand 2S/3S, you go for 3S (More power for same current as voltage is high).
So, you can get C capacity and mAH Capacity

Now, ESC Current capacity = motor max current x (1.25-1.5).
And battery should safely discharge that current of motor (Mot. Current = .75 x Battery stable current).

And above all, prop can increase or decrease the loading pattern.
Always use proper prop suitable for that motor.
If, 10x6 and 10x4.7 is given, select 10x4.7 first to stand in safe side.If pitch remain same with Dia variation, select lower dia prop.

Thanks

Thank you Kalyan..for the nice explanations...

+1 KALYANPRODHAN