The White LED turns ON before it gets fully charged.
What is telling you that the battery is not fully charged.
Why does the charging occur in few second intervals and not at one go?
Depends on if the battery is actually fully charged or not, something is telling your charger that the battery is full, the charger stops charging the battery, the power begins to drain, the charger detects the drop and begins to charge the battery again.
Couple of questions for you;
Do you continually use the notebook with the battery in place and the charger turned on.
If you disconnect the charger and use only the battery to power the notebook how long does the charge in the battery last.
If you remove the battery and use the AC adapter to power the notebook, does the LED still change colour.