hansika, packs are not easy to charge, you would have to charge each half of the lithium pack separately, so you'd have to charge each series string isolated from each other using a single charger. You can not charge lithium batteries in parallel safely without much more advanced charge control, even in series you should monitor each cells voltage seperatly.
The typical charging scheme for a single Lithium cell is a constant current source of 1/2 to the full mah capacity of the cell until the voltage of the cell reaches 4.1 volts, and then you supply a constant voltage of 4.1 volts until the charging current reaches 1/10th of the cells capacity. Something else to consider is you have to monitor the battery for under voltage as well. Thermal monitoring of the cell is advisable as well, because under normal charging conditions a lithium battery will NOT heat up when it's charged, they have a 99.8% charge efficiency. If it heats up during charging it's a sign that there is something seriously wrong. Over charging and over discharging the cell will cause the chemicals inside to either passivate or plate out to and the cell becomes useless.