How long should I recharge my drill's batteries?
I have found the original instructions on this page. 


  After approx. 3 hours of charging, the battery will be sufficiently
  charged for use in regular applications. After approx. 8-10 hours of
  charging, the battery will be fully charged.


After a few lines, it says:


  After normal use, a charging time of 3 hours will provide sufficient
  power for most applications. However, further charging for up to 6 hours 
  could significantly increase the use time, depending on the
  battery and charging conditions.