Nokia X2 - 01 — Poor battery backup

Address:

South 24 Parganas, West Bengal

Dear sir,
i bought a nokia x2-01 one month ago,iam getting very very poor battery back up when using net, every time after being fully charge the battery goes empty within 3to 4 hours of net using if net is not used then it gives long back up of 3 days
1.is this the problem of battery?
2.is this the problem of the set?
Its make me very dissapointed for nokia